Nodes don't have to keep transactions in their mempool. Each node can have its own settings. There are many nodes that use default settings and drop unconfirmed transactions from their mempool after 14 days.

That's how it has been designed.
I think if you don't open your wallet, mycelium will no longer rebroadcast your transaction.

Yes.


With just connecting your internet connection when signing the transaction, you don't really increase your security. For more security, you should import your private key into a wallet on an air-gapped device.


You should have two wallets. One created with your private key on offline device and a watch-only wallet on an online device.

Here is a good guide.
How to spend from an offline paper wallet using Electrum

I have never used the website in question and I would avoid it even if it was working.
You should never use online websites for generating a bitcoin address.

If you want to have a bech32 bitcoin address, install a trustworthy open source wallet like electrum or Sparrow and create a wallet. In this way, you can have multiple addresses all generated from a seed phrase.
For more security, It's recommended to generate your wallet offline on an air-gapped device.

If you are on the desktop version, click on the circle located at bottom right corner of the window. In the new window, go to "Proxy" tab.
If you are on the mobile version, tap on the circle located at top right corner of the screen. Go to "Network" and after that tap on "Proxy settings".

You don't need to use a wallet that supports bitcoin along with the forked coins.
Import your private key into a wallet that supports bitcoin and move your bitcoin. After that, you can import your private key into a wallet that supports the forked coins to spend them. 


Here are some tips for ensuring the security of your fund.

• Use a trustworthy open source wallet.
  
• It's recommended to import your private key into an air-gapped device and sign your transaction offline.
  
• First move your bitcoin and then go for forked coins.
  

The fee you pay for sending bitcoin from an uncompressed address is slightly smaller than the fee you pay for sending bitcoin from a compressed address.


First note that when we say "uncompressed address", we mean that the address has been derived from an uncompressed public key and when we say "compressed address", we mean that the address has been derived from a compressed public key.

You can generate different legacy addresses using each of compressed and uncompressed formats of your public key. They are both standard and you can use each of them. It's recommended to use the compressed address.

When it comes to bech32 addresses, you can still generate different addresses using each of compressed and uncompressed formats of your public key, but the one that is generated from the uncompressed public key would be non-standard and it would be very difficult to spend fund from that.

You are wrong.
You can send bitcoin from any type of address to any type of address you want. This means that you can send bitcoin from segwit address to legacy address and vice versa.

We have compressed and uncompressed addresses, because the public key can be either compressed or uncompressed.
When bitcoin addresses were introduced for the first time, they were all derived from uncompressed public keys. In 2012, it was decided to generate addresses from compressed public keys to decrease the transaction size.

An uncompressed public key includes 130 characters, while a compressed public key includes 66 characters and takes less space.

If the address is yours, you can know that with checking the public key or the private key.
If there's outgoing transaction from the address, you can know whether the address is compressed or uncompressed with checking the raw transaction.

If the address is not yours and there's no outgoing transaction from the address, there is no way to know whether it's compressed or uncompressed.

Tap on "Receive" button and "Create request". Select "Address" and you will see a QR code which contains your address.
You can tap on the "QR code" to see the address itself.

Take note that every time you do this, electrum gives you a new address and they all are yours.
To see all your addresses in one place, tap on your wallet name at top left corner of the screen and go to "Address/Coins".

With using TOR connection, you can hide your IP address, but you would still rely on a third party for getting transactions data and broadcasting transactions. The server you are connected to can link all your generated addresses with each other.


Your security depends on the security of the your device, how you generated your wallet and how you keep you keys. When it comes to security, it doesn't matter whether you reuse addresses or not.

Coins tab displays your coins and the address associated with each of them. The coins you own are associated with two of your addresses and all addresses are empty. That's why you see two address in Coins tab.
Once a new address of your wallet receives fund, you will see the third address in coins tab.

For making a transaction offline, first you create an unsigned transaction on your watch-only wallet. Then you export the unsigned transaction and import it into your offline wallet. You sign the transaction on the offline wallet and after that you import the signed transaction to the online device and broadcast it to the network.

A paper wallet should be generated offline and the private key should never connect to the internet. Otherwise, you would defeat the purpose of a paper wallet.
If you generated your paper wallet using on an online device, that's not really a paper wallet.

You can import your private key into a hot wallet and spend your fund, but that's not recommended. For more security, it's recommended to import your private key on an offline device (preferably to be air-gapped) and sign your transaction there.
Take note that for making a transaction offline, you would need two wallets. You would need to create a wallet with your private key on an offline device and a watch-only wallet on an online device.
The offline wallet is used for signing the transaction. The online wallet is used for creating the unsigned transaction and broadcasting the signed transaction.


I edited the post to fix a typo.
Thanks Roberto12345 for the correction.

I mean the address which has been generated by your private key in electrum. Is that correct?

As I already said, to check the address generated by your private key, you can tap on your wallet name at top left corner of the screen and go "Addresses/Coins".

- Is the derived address also correct?
- Is the wallet synced? (If the wallet is synced, the circle located at top right corner of the screen should be green.)
- Did you check the transaction history of the address on a block explorer?  Is there any transaction associated with the address?

Tap on your wallet name at top left corner of the screen and go "Addresses/Coins". After that, you will see a bitcoin address. Is the address same as your paper wallet address?
If the address is not correct, either you entered a wrong private key or imported a correct private key but with wrong script type. Note that if your address starts with bc1, you should add "p2wpkh:" before the private key.


I edited the post to fix a typo. Thanks Charles-Tim for the correction.

Wrong.
As I said in the first reply, transactions are confirmed by miners.

Transactions must be valid, so that they can be included in the blockchain, but it's not that a transaction is included in the blockchain once it's validated.
For a transaction being confirmed, it's required that a miner (or a mining pool) solves the proof of work problem, mines a block and includes that transaction in the block.

A transaction can be partially signed, if you are using a multi-signature wallet.

If your wallet is m of n multi-signature wallet and m is greater than 1, you have to provide more than 1 signature for each of UTXOs you are trying to spend. So, your transaction is partially signed and it needs to be singed by cosigner(s) as well. To do so, you should export the partially signed transaction and import it to the cosigner wallet.

You are completely wrong.

Please always read previous replies before making a post.
As already stated, the transaction size and the fee doesn't depend on the amount you send. Therefore, it doesn't matter you are spending 1 BTC or 0.1 BTC.
What matters is the number of inputs and outputs.

Every time you make a bitcoin transaction, you broadcast some data.

For example, for each input you add to your transaction, you should have a TXID, an index and an unlocking script in the transaction data. Also, for each output you add to your transaction, you should have a value and a locking script.
The more inputs or outputs you have in your transaction, the larger data you have to broadcast to the network and the larger data the miner has to include in the blockchain.

(The raw transaction should include some other data and what I mentioned above are just some of them.)