Depends, if the wallet isn't HD (Hierarchical Deterministic) (Ex. Bitcoin Core Wallet), the answers are:
[1] Yes
[2] Yes
[3] No
Encryption won't affect the new address (private key) generation of the wallet, any new generated addresses after the separation are randomized which will produce different new addresses for wallet A & B.

If the wallet is an HD wallet with a SEED (Ex. Electrum), it's:
[1] Yes
[2] No
[3] Yes
Any new Private keys are based on the wallet's seed so, if you generate more addresses, both A & B wallet will produce the same.

Last time I checked, you can request in the UI of blockchain(dot)info for the private key of any of your addresses.
Doing this will remove that address to the list, but it's still best to send all the funds to a new address to be safe.
Given that, the logical solution when shifting to a different wallet is to just send all of your funds to the new wallet (ex. Electrum) via transaction.

<I'll verify this later> Edit
Nah, Export private key is only available for their Ethereum Addresses.

Also, this should be moved to Service Discussion > Web Wallets.

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As for the thread question:
For newbies, it is safe in the sense that you don't have to take care of the backups and private key managements and the fees to use bitcoin, all you need is the backup seed or your key+passphrase and your email address.
But not safe in sense of security, on that website, your bitcoins aren't totally under your control.

There isn't much difference between brutforcing private keys and the mnemonic seed in terms of the total number of combination.
But yes, an HD wallet's seed has lower security but still, collision is impossible.
Here's an old thread to clear things up: How HD wallet works for back ups? Reply by achrow101

Here's a short answer: There are total of 5,444,517,870,735,015,415,413,993,718,908,291,383,296 possible combinations which makes any random combination unique.
Using that, it's easy to compute the chance to get a collision using a calculator that can enter 40+ characters.

Actually, he didn't have any investments, he's looking (seemingly begging) for investors.

Investors aren't helping developers, teams, corporations or businesses, they are investing.

This could help you at least:
If you're confident that your script is working and useful, make a demonstration or a whitepaper to encourage potential investors to "help" your project, this thread wont do.
Or sell the script alongside with the demonstration or documentation on how it works.

Hope this helps.

P.S: Yep overthinking does hurt heads, pulsating physically.

You can't spend using that "watch only" imported wallet.
If that's possible, anybody else can just steal someone else's funds just by importing addresses with huge balance.

The only options you have to restore a spendable wallet are:

• The Seed that you've instructed to write down during the first wallet creation process.
• Each of the Addresses' private keys.

The addresses are always visible to the public, example: blockexplorers.
By the way, if you're not sure: Addresses starts with 1, 3 or bc1 ; Private Keys Starts with 5, K or L ; and the SEED consist of words like dog sheep life science geek maid...etc.

Drag and drop it to a new tab or window to view full screen, (after checking) that image has 1920x1200 dimensions which is pretty big to blur.
Here's a link of the full screen version: Right Click->Open Link New Tab

You can try using Vanitygen or Oclavanitygen to waste your electricity, time and dignity; but the chance to bruteforce a loaded address is almost impossible.

Yes, of course. Anyone can pick a random number manually even without a computer.

Regarding Electrum, since it's a HD wallet, private keys generated by it were based on the SEED, it's using 12 words as default (docs.electrum.org).
With that, hitting a collision isn't possible, there are more possible combinations of Electrum's 2048-word Dictionary (with different language variations) than the total population of the world.

No that's too few, add more Zeroes.

Have you tried -rescan as aleksej996 said?

Otherwise, it means that the address didn't belongs to the wallet, I think you know this.
The first paragraph from the OP strongly suggests that it is an old backup.
Most likely, you've unintentionally overwritten the most recent wallet.dat by an outdated backup during your copy-paste procedure.

I'd say, stop looking at charts, not until exchanges become free of manipulation (more even, based from stock exchange).
Even if anyone can polish his chart "technical analysis" skill to "convincing" level, current Cryptomarket is still a different field.
When the whales do their jobs, every prediction could fail to deliver its promises.

And a triple bottom happening in Bitcoin market is far fetched idea.

Yes it may, as long as you've send the second transaction using the same inputs right after the first with larger fees.
The first transaction must still be unconfirmed to do that.

In addition, a typo will make the final address invalid (to the checksum) that will disable the send button.
You can produce a valid address through typo if you're the world's most unlucky fellow.

Even thousands of private keys wont make a wallet.dat file size grow to 1.5Gb, that's insane.
Are you sure that it is a wallet file? The file name is just wallet.dat or renamed? You're certain that it was your backup, or it was salvaged?

Because you see, there are other files that ends with ".dat" extension, if you just recovered it from a formatted disk or old hard disk, the chance that it's not a wallet.dat is high.
Loose Files from windows applications sometimes named with .dat extension, and a Gigabyte of generic file must be a part of an app.

I do not know the set up of your Altcoin but,
"0/offline" error can be caused by a non-synced node and the user tried to make a transaction if the client enables him to do so.
How much premine did your Altcoin has? And was the client that you're testing 100% synced?

Honestly, it's my first time seeing "-1 confirmation" on Electrum.
Normally, transactions are either Unconfirmed or 1+ Confirmation.

Make sure that you're using the official Electrum app, not "Pro" or a clone. The original version can be downloaded from Electrum.org.
If you've downloaded yours from electrum.com or other sites, that must be fake.

6x RX 580s (185W x 6) is an overload for a 1,200W PSU.
Even though that model has 100A on its +12v rail, it is still at its peak with a 1110W load (only have 90W window).
Since you're mining Ethereum, it's alright to underclock to lower the power consumption, or use only 5 GPUs for now.

And this bugs me: "my friend has two rigs with 2 x 6 RX 580 sapphire nitro 8gb"
Two rigs with 2x6 RX580, means 12GPU in each rig? No, right? so 6GPUs each.

The error is pretty normal and shouldn't cause a reboot,
both of the rigs seems out of juice that can trigger a shutdown but your BIOS was set to restart whenever the system was abruptly powered down.

The airflow is way too weak to remove the dusts from confined spaces and corners.
Compressed air is the best choice, but for a practical solution, yes Hair dryer on cold setting will do the job.

But any of these can't remove the stuck dusts on the fan's surface, I'm using cotton swabs dipped in alcohol to clean them thoroughly.

I'm sorry, I mistook your post as a "stopped synchronizing" post.

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I did a quick research and I think it has something to do with SegWit (August 24, 2017).
Also, I have checked the blocks included in blk00971.dat & I've noticed that the timestamps range from last week of August to Mid September 2017.
And blk00975.dat's blocks are from September 2017, one month after SegWit (BIP144) activation.

SegWit input/output scripts structure is a lot different than the regular transaction's.

That "parser" doesn't support and cannot read SegWit Txs.
Disclaimer: I could be wrong.

Quoted and Verified.
You may need to know the proper way to post quoted messages to avoid confusions, just follow TMG's post format above using [code][/code] tag.
It will be useful for you in case of a verification is needed.

The block cluster must be corrupted due to some reasons.
Try to delete blk0097X.dat from the default data directory then re-sync your node.
For Windows, open file explorer/my computer and browse to: C:\Users\"UserName"\Appdata\Roaming\Bitcoin

I would like to clear one thing: Electrum isn't hodling your bitcoins, it holds the private keys to control the bitcoins (inputs) that technically belongs to you.
Bitcoins are recorded (stored) in the Blockchain.

Yes, you are. But it will troublesome for him to copy-paste->enter each of the addresses.

The easier way is to open it using Electrum (it's too easy to download and install/open)
Display the address tab and find the addresses with balance, those are the addresses that should be checked on blockexplorer site.
Or use pooyah's link.

Ouch ok, so it must be an inside job or a sophisticated hacking incident and the attacker must have stolen more than customer's emails and contacts.
Otherwise, the "other guy" was right.

The first statement suggests that the hacker(s) didn't just fetched the emails but also Bitmain's admin accounts (and administration rights?) as well.

This is more serious than I thought.