Lots of questions. Help me get up to speed

[glowinthedarkcia]

I was very active in this community many years ago but I dipped after some life stuff. I need to be brought up to speed on several stuff.

1.) Does anyone even use the bitcoin q / core desktop app anymore? I remember I'd always have the whole blockchain downloaded and run the official client, but it seems that people favor "online clients" these days if that's correct terminology? Blockchain online but wallet stored on client to save room? I figure that's a must for mobile apps now?

2.) Mobile apps. Which is a good android client for bitcoin?

3.) I have lots of very old (2013) private keys generated on paper wallets from bitaddress.org with bitcoin on them. How do I go about importing them? Is there a good mobile app for importing older non-passworded private keys?

4.) Maybe I should use a desktop client to import the keys in a safe linux machine rather than android? Is there an "online" version of a desktop app so I don't have to download the whole blockchain?

5.) Is it any more or less secure using online clients vs having the blockchain fully downloaded?

I mostly tuned out of all latest updates, releases, security vulnerabilities since around 2015. Is there any news I should be up to speed on? I'm still trying to wrap my head around DeFi, NFTs, smart contracts, and all sort of new protocol lingo. Also Lighting/L1?

[Tanaka-Wun]

I was very active in this community many years ago but I dipped after some life stuff. I need to be brought up to speed on several stuff.

You were very active in this community before?
First of all, Welcome back! But how come this account is new? Who are you before(old account)?

[mk4]

1. Running your own node is always recommended, but I think it's unrealistic to expect the masses to be running their own node. Unfortunately most people will just stick to Coinbase/Binance simply due to ease-of-use.

2. https://bluewallet.io/

3-4. Not sure about mobile, but probably Electrum on desktop.

5. You'll be totally fine with using non-custodial software wallets like Electrum. Stay away from the likes of FreeWallet and such.

[ice18]

2.) Mobile apps. Which is a good android client for bitcoin?

Mycelium works great for me on my android app, been using it for some years now no problems encountered, I think this is one of the most secured btc mobile wallet that I've used. You can import your keys easily and use it without downloading the whole btc chain, just like Electrum in PC as mentioned by @mk4.

[Oshosondy]

People prefer the normal wallets that does not need to download the blockchain because the blockchain gigabyte is very large, over 400 gigabyte which many people can not afford, they just download the one that does not need the blockchain to operate which are still noncustodial wallet.

Electrum is a good mobile bitcoin wallet app, get it on the official site https://electrum.org

You can import private keys generate on paper wallet to electrum, electrum support it.

You can use android but make sure your phone is not having malware, but using Linux will be better and will be what I will recommend.

Just know that anytime you are online, protect your device, that is the main thing.

[NeuroticFish]

1.) Does anyone even use the bitcoin q / core desktop app anymore? I remember I'd always have the whole blockchain downloaded and run the official client, but it seems that people favor "online clients" these days if that's correct terminology? Blockchain online but wallet stored on client to save room? I figure that's a must for mobile apps now?

Although maybe not necessarily on mobile, SPV wallets have a big "market share".
But the later news made more people realize that they can be tracked and some more may have started using Bitcoin Core again (or their own servers, which need Bitcoin Core).
Also, let's not forget that far too many users (still) keep their funds in custodian wallets, usually exchanges.

2.) Mobile apps. Which is a good android client for bitcoin?

I use (rarely) Mycelium. It has (plenty of) room to improve (to be overly nice), but it's not a bad wallet and it's one of the very few that support hardware wallet, which imho it's a must, especially on mobile phones.

3.) I have lots of very old (2013) private keys generated on paper wallets from bitaddress.org with bitcoin on them. How do I go about importing them? Is there a good mobile app for importing older non-passworded private keys?

Mycelium can do that. But.. just read forward  

4.) Maybe I should use a desktop client to import the keys in a safe linux machine rather than android? Is there an "online" version of a desktop app so I don't have to download the whole blockchain?

Yep. Safest would be to not import them into anything that's online. If it's big funds please stay on the safe side.
Learn the basis of cold storage and import the private keys onto a system that will never go online (it can be even a Linux on an USB stick) and keep only the addresses in a view wallet online. It's enough for spending safely. Tails OS with Electrum can be such a choice, but you'll have to read about persistent storage there (and always keep a copy of the keys or seed safely, maybe on paper).
Also consider buying a hardware wallet (and move to HD wallet, based on seed). Hardware wallets are pretty safe and pretty convenient too, especially if you're not a tech guy.

5.) Is it any more or less secure using online clients vs having the blockchain fully downloaded?

If you use SPV clients your funds can be tracked to you. No other big problems.
The coins can be stolen from you with or without Bitcoin Core if your system is not secure or you make mistakes (like keeping the keys "safely" in the e-mail)

I mostly tuned out of all latest updates, releases, security vulnerabilities since around 2015. Is there any news I should be up to speed on? I'm still trying to wrap my head around DeFi, NFTs, smart contracts, and all sort of new protocol lingo. Also Lighting/L1?

I'd start with cold storage, hardware wallets, SegWit and Lightning, especially as you have bitcoin.
Ah, please give a minute to the reading about clipboard hijackers too.
Then you can move on to altcoins/DeFi and such, although keep in mind that many of those may be just money traps (you can read about ICO era).

[o_e_l_e_o]

3.) I have lots of very old (2013) private keys generated on paper wallets from bitaddress.org with bitcoin on them. How do I go about importing them? Is there a good mobile app for importing older non-passworded private keys?

4.) Maybe I should use a desktop client to import the keys in a safe linux machine rather than android? Is there an "online" version of a desktop app so I don't have to download the whole blockchain?

NeuroticFish is right here - you should only import your private keys on to a clean OS with a freshly installed wallet on an airgapped computer, to maintain their security. The best way of doing this is to use an old computer or laptop, disconnect the WiFi card and unplug any ethernet cables, format it, install a Linux distro of your choice, then download and verify Electrum on another device and transfer it to your airgapped device using a formatted USB drive. Alternatively, after airgapping you can boot to Tails from a live USB which has Electrum pre-installed. You'll need to create a complementary watch-only wallet on an internet connected device which contains only your addresses so you can view your balances and create unsigned transaction, which you then move to your airgapped device via a USB drive to be signed by your private keys.

However, the main question is "What do you want to do with any coin that is on these private keys?" If you just want to see what you have but not actually spend it, then I would suggest not importing the private keys anywhere and keeping them on the paper wallet. The paper wallets should also have an address you can look up to view your balance.

[dkbit98]

Does anyone even use the bitcoin q / core desktop app anymore?

Many people are still using Bitcoin core wallet, including everyone who runs their own bitcoin node and have full blockchain downloaded.
This is the best option if you don't want to trust any SPV wallets and other people nodes with your transactions.

Mobile apps. Which is a good android client for bitcoin?

I would only use android wallets for keeping small amounts of pocket bitcoin money, and many of them are closed source that I don't recommend.
Electrum and Mycelium android wallets are open source, but I prefer how Blue Wallet works.

I have lots of very old (2013) private keys generated on paper wallets from bitaddress.org with bitcoin on them. How do I go about importing them? Is there a good mobile app for importing older non-passworded private keys?

I would not import those private keys in any mobile wallets, better use offline Electrum wallet (you don't have to download complete blockchain for that).

[witcher_sense]

I was very active in this community many years ago but I dipped after some life stuff. I need to be brought up to speed on several stuff.

1.) Does anyone even use the bitcoin q / core desktop app anymore? I remember I'd always have the whole blockchain downloaded and run the official client, but it seems that people favor "online clients" these days if that's correct terminology? Blockchain online but wallet stored on client to save room? I figure that's a must for mobile apps now?

As for the question of whether to have your own copy of blockchain or not, it is always a personal matter. In my view, rational people, especially those concerning about privacy, security, decentralization, self-sovereignty, etc, should have their personal full nodes running. There are multiple implementations of bitcoin full node besides Bitcoin Core, so you don't necessarily need to use an "official" client for that. You can connect your mobile bitcoin wallet to your personal bitcoin full node instead of third-party servers so that a wallet provider will have a lot less information about your transactions and your real identity.

[rosenbauer02]

Some are still using bitcoin core but many people prefer to use non-custodial wallet which doesn't need to download whole blockchain which takes up a lot of space. There are wallets you can use like electrum, trustwallet and many more wallet that are non-custodial.

[NeuroticFish]

Some are still using bitcoin core but many people prefer to use non-custodial wallet which doesn't need to download whole blockchain which takes up a lot of space. There are wallets you can use like electrum, trustwallet and many more wallet that are non-custodial.

It would be nice if you'd start by learning what custodial wallet means.
Hint 1: it's not about downloading blockchain or not (actually if you use custodial you never have to download the blockchain)
Hint 2: Bitcoin Core is not custodial

[LoyceV]

I was very active in this community many years ago

Feel free to share, did you have an account here before?

3.) I have lots of very old (2013) private keys generated on paper wallets from bitaddress.org with bitcoin on them. How do I go about importing them?

My advice: only import them when you're planning to use/move the coins. Depending on the value you sould consider this:

I was considering Electrum, only downside is that when creating a wallet, seed creation is exposed

Online:
Install Electrum on your PC.
Import your address to create a watch-only wallet.
Preview the transaction, Copy the unsigned transaction. Put it on a USB stick.

Offline and running without hard drive storage:
Get a Linux LIVE DVD. Use Knoppix for instance, or any other distribution that comes with Electrum pre-installed.
Unplug your internet cable. Close the curtains. Reboot your computer and start up from that DVD. Don't enter any wireless connection password. Keep it offline.
Start Electrum. Import your private key.
Copy your unsigned transaction from the USB stick, load it into Electrum.
CHECK the transaction in Electrum. Check the fees, check the amount, check all destination addresses (character by character).
If all is okay, sign the transaction. Copy it back to your USB stick.
Turn off the computer. That wipes the Live LINUX from memory and all traces are gone.

Online:
Use your normal online Electrum to (check again and) broadcast the transaction.

Bonus:
After moving all your Bitcoin, and once the transaction confirmed, check if you own Forkcoins.

My 2 sats about wallets: I use many: Bitcoin Core, Electrum, Mycelium, BlueWallet, Phoenix Wallet, hardware wallet, paper wallet, Coinomi and probably a few more I forgot now. It depends on personal preference, and on the value you want to store. It doesn't hurt to try a few.

[mk4]

Some are still using bitcoin core but many people prefer to use non-custodial wallet which doesn't need to download whole blockchain which takes up a lot of space. There are wallets you can use like electrum, trustwallet and many more wallet that are non-custodial.

Just a heads up:

1. Bitcoin Core is also a non-custodial wallet
2. You don't necessarily need to download the entire blockchain if your computer doesn't have enough memory. Lookup pruned nodes, where you can only download like 15gb and such.

[khaled0111]

2. You don't necessarily need to download the entire blockchain if your computer doesn't have enough memory. Lookup pruned nodes, where you can only download like 15gb and such.

I am sure you already know that and it's just a miswording, so I want to clarify that even if you set up a pruned node, you will have to download the whole blockchain but only the most recent blocks (depending on your configuration) will be saved on your device. The minimum storage size you can set is 550Mb (-prune=550).

I have lots of very old (2013) private keys generated on paper wallets from bitaddress.org with bitcoin on them. How do I go about importing them?

OP, if you are going to spend your Bitcoin or move it to a new wallet, don't forget to claim your fork coins. Here is a guide on how to do that safely:
LoyceV's Bitcoin Fork claiming guide (and service)

[SFR10]

1.) Does anyone even use the bitcoin q / core desktop app anymore?

I actually "started using it this month"

but it seems that people favor "online clients" these days

Most of those users are probably newcomers and for the veteran users who still prefer using such wallets, it's a trade-off between security ^{[+ a few other things]} and convenience.

5.) Is it any more or less secure using online clients vs having the blockchain fully downloaded?

Online clients/web wallets are always less secure, but that doesn't mean the latter is completely risk-free ^{[it depends on the situation]}!

• Here are a few more risks in addition to ETFbitcoin's comment:
  
  • Some of the web wallets are prone to having display bugs ^{[e.g. zero amount is shown, despite viewing your funded address on explorers]} that prevents you from using your funds!
  • If a hacker infiltrates their platform, there's a high chance that you'd lose your funds!
  • In some/most of the web wallets, you don't actually own any of the funds that you see in your wallet ^{["not your keys, not your coins"]} and if something was to happen to their website ^{[e.g. inaccessible]}, then you'd not be able to spend your funds on that moment.

I mostly tuned out of all latest updates, releases, security vulnerabilities since around 2015. Is there any news I should be up to speed on?

The following link might come in handy: Bitcoin Improvement Proposals ^{[scroll down]}