The keypool has been increased to 1000. The wallet maintains the keypool at 1000 as long as your backup is from a recent version of Bitcoin Core. It's generated every time the wallet has been unlocked. You can back it up whenever you want and that backup will be valid for 1000 transactions. The general consensus is to back it up every 100/1000 transaction since your addresses will definitely be used up by then.

No. No matter what you do, you cannot steal BTC. Spending BTC requires the correct signature to spend it. If the signature doesn't tally with the conditions for the inputs to be spent, then it isn't possible for anyone to spend any BTC. You can steal money in a sense that you can "re-spend" coins that were in another blockchain that is recognised by the merchant by essentially replacing that blockchain.
Bitcoin would be dead already before they start to censor transactions. No one would use a coin for which someone obviously has the say to which transactions they like.

Depends on when you've created the wallet. If you've created the wallet (not restore) recently, then you probably just need one. If it says HD at the bottom right, one backup is enough, unless you change or set a password.

If you've created the wallet a long time ago and the bottom right doesn't have the HD symbol, you need to backup per 1000 or 100 transactions, depending on your configuration.

Go to your Electrum client > History and find your unconfirmed transaction. Right click the transaction, press detail and copy the Transaction ID line in the popup window. Paste it here for us, if you don't mind a slight loss of privacy.

Bitaddress.org, bip38.org or Electrum. Generating anything with only a passphrase to access it is incredibly insecure. If you really do want to use something like Brainwallet but more secure, try going to keybase.io/warp/. You are to select your own secure passphrase and add an email with your salt. I wouldn't say that its super secure but its definitely more secure than typical brainwallet since the attack has to be specific at you.

Not safe at all. Blockchain.info is notorious for messing up the funds of their user and they shouldn't be trusted with any Bitcoins.

Did you receive the backup seed? AFAIK, the backup seed is compliant with BIP39. If you want to extract it, go to https://iancoleman.io/bip39/ and key in your seed. You can find the account number (ie derivation path) from settings>addresses.

Your wallet is no longer safe. Please do not use any addresses with that seed again.

I've taken the initiative to look at the keys first and it doesn't seem like you have any significant amount of Bitcoins after fees so I didn't try to secure them.

Download Electrum from Electrum.org. Install Electrum and open it, select Standard Wallet> I already Have a seed and key in your seed. Next, go to option and press BIP39.

The addresses are the hash of the public key.
There is actually 2^96 private key that corresponds to an address.
Yes. Of an address that is generated by someone else already.
That's like finding a needle in an ocean of haysack. You can generate the same addresses again if your RNG is flawed and it isn't random. There are easier ways to steal coins than this.
Yes. Most people don't get the concept of the possibility. If something is possible, it doesn't mean that its remotely likely to happen. Its more likely for me to get struck by a lightning multiple times in consecutive years while sitting on a toilet bowl than anyone ever generating a collision of an address that is generated securely.
Make sure your address is truly generated randomly. /thread.

Since your peers would only have 8 outgoing connections max, you would be hogging their connection if you have a relatively slow connection. Depending on what you do with your computer, the connection would become significantly worst. Its okay to run a full node with port 8333 but it wouldn't be all that good to have a slow bandwidth.
The relaying of transaction would probably be okay for your bandwidth. Your latency would matter more in that case.

Peers would only disconnect if you're unresponsive/misbehave. I doubt they really care about your bandwidth but their download would be a lot slower if everyone who has a slow internet runs a node.

Have you changed the data directory of the wallet? Your wallet.dat might be incorrect which would explain why the transaction isn't showing.

Go to Help>Debug window>console and key in this
.

If the ismine returns true, then you don't have to be too afraid.

Yeah. Go to Keys and copy the private key out. Go to Electrum and create a new wallet. Select "Import Bitcoin private keys or addresses" and key in this:
.

You must replace the L5T... with your own private key.

Coinb.in wallet offers bech32 addresses (addresses starting with bc1), P2SH addresses (addresses starting with 3) and legacy addresses. Which one are you using?

If you're using an address starting with bc1 or P2SH, you're out of luck. I don't think there is any standard of signing messages with them. If you're using legacy, go to Keys and press Show beside the private key. Copy the whole key out and go to the sign tab and paste your private key in the corresponding space and type your message.

How many times do we have to tell you? http://lmgtfy.com/?q=is+it+possible+for+a+bitcoin+address+collision+to+happen%3F

No. It is not impossible but the chances are way too low. Its widely known that there is a higher number of addresses (2^160) that could be generated than the grains of sand on earth and you're more likely to be struck by a lightning 10 times while sitting in a toilet bowl for 10+ years in a row, IIRC. You would have better chance winning the lottery a few times for consecutive years than to generate a single collision.

The upload bandwidth is extremely low and it doesn't really make sense for you to run a full node since it doesn't necessarily help the network. Peers would have your node as a bottleneck when they download their blocks when they can connect to better peers. You would have to netlimiter to try to limit the bandwidth Bitcoin Core can use. Bitcoin Core only has the parameters to limit total network usage.

If you aren't too concerned about security and privacy, you can always use a SPV client as your wallet.

Depends on how many consecutive blocks you want to mine. You have a good chance to mine 2 consecutive block with say 30% of the hashrate but mining 3 consecutive blocks would be significantly harder, hence the formula.
Possible. Is it worth the effort though? As long as they have 51% of the network, they can outpace the entire network by themselves. The attack is somewhat covert since the attack is not known until it actually happens. Their main goal isn't to get the most amount of Bitcoin but it is to attack Bitcoin. Bitcoin wouldn't have much value after the attack anyways.

Difficulty changes every 2016 blocks and the time to mine the remaining of the total coins would still take about the same amount of time.

Is the -1 confirmation showing on Electrum or on your mixer website?

If its on Electrum, try upgrading it or change a server by going to the bottom right dot> Server> Uncheck connect automatically and right click on any server to choose it. It should be able to synchronize; for the latest version.

If its showing on the mixer website, contact them. It's likely that your transaction has been dropped and the mixer is glitching out.

A currency is used for trading and purchasing goods. Bitcoin can be considered as an asset. How many people actually uses Bitcoin to purchase goods? Bitcoin has mostly just become an investment option and it isn't wrong to classify it as an asset. I doubt South Korea's adoption is all that high to classify it as a currency anyways.

6 confirmation prevents any attackers without 51% of the hashrate from trying to reverse the transaction. If you have more than 51% of the hashrate, you can reverse any transactions, no matter how old it is.

Using irreversible for 6 confirmations doesn't seem right.

Confirmations basically shows the number of blocks that has been mined ontop of the block that has included the transaction. Confirmations will never be enough for a transaction to be considered irreversible. The higher the number of confirmations simply mean that it would be harder for any attacker to reverse the transaction.

The clock icon simply denotes the number of confirmations and when its full, it would be green and it would have 6 confirmations which is relatively safe (other than in 51% attack).

Did you check the denomination of the BTC you've sent?

Certain wallets uses mBTC (milibitcoins) as opposed to Bitcoin as a denomination. 1mBTC =0.001BTC and your wallet might have displayed the dialog as mBTC and you keyed in 0.014mBTC instead of 1.4mBTC. At any rate, put your TXID either privately to a trusted user or publicly and we will know what went wrong.