Remove 2FA in Electrum and use Standard Wallet instead.

[HCP]

The more the inputs and outputs, the more the fee. The second output will likely be the change address (the address you will receive your change). The difference in the fee will be minimal.

The output is the number of addresses that you are sending to. If your coin has change, it would be sent to the change address.

I can't understand the part that is in bold. I'm confused, sorry.

Bitcoin isn't stored as just a "sum" number like cash in your bank account... it's stored in "chunks" called UTXO's (Unspent Transaction Outputs). So, every time you receive some Bitcoin, you get another chunk added to your collection. When you want to send someone some Bitcoin, unless you have a chunk that is exactly the right size to cover the amount you're sending + fee, then there will be leftovers... this is called "change" and is simply put back in your wallet as a new (smaller) chunk.

Let's say you have chunks worth 0.1, 0.2 and 0.3 BTC... you decide you need to send 0.15 to someone. You don't have a chunk that is exactly 0.15... so your wallet will use either the 0.2 or 0.3 chunk (depending on what sort of UTXO selection algorithm your wallet uses).

Let's assume your wallet uses the 0.2 chunk. Your wallet will create the transaction and says please send 0.15 to AddressA... and put the remaining 0.5 back in my ChangeAddressY (we'll ignore fees for now).

More reading here: https://en.bitcoin.it/wiki/Change
and here: https://en.bitcoin.it/wiki/Coin_analogy

Basically, unless you spend the exact amount of some combination of chunks, you're most likely going to have 1 extra output on any given transaction (which is simply the "change" going back to your wallet).
 

Note: The number of Outputs has a very minimal effect on the data size of a transaction compared with the number of Inputs which will have a much greater impact on the data size of transaction (and hence will affect the total fee more).

The reason for this is that an Input typically has 2-3 times the data size of an output. For instance, with transactions using older bitcoin addresses (P2PKH) an input would be around 148 bytes... and an output would be about 34 bytes. Newer addresses are slightly less.

Unless you're sending to multiple people in 1 transaction (like an exchange doing a batched send), chances are that the data size of your inputs is going to be far greater than the data size of your outputs.

This is why receiving a lot of small BTC amounts ends up costing a lot in fees to move... if you have 10x chunks of 0.01... and you want to send 0.1 BTC, you suddenly have 10 inputs and your transaction data size is going to be quite large and require a very large fee.

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If you want your transaction to include only 1 output, you should spend the entire balance of selected UTXOs, so that your transaction doesn't have any change.

So what I need to do is just send the maximum amount of the current multi-signature wallet to a standard wallet, right?

Thanks again for the help.

Correct, send the maximum amount in 1 transaction. If you use the max button in Electrum (or set the amount value to ! ) it will automatically calculate that "max" value for you based on the total amount in your wallet - minus the transaction fee.

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If you disable 2FA, your wallet would be still a 2 of 3 multi-signature wallet, but with two master private keys.

Of the 2 master private keys, one of them is for my receiving wallet address, is that correct? and the other one is?

I feel you don't know how a multi-signature wallet works.

The standard wallet you create on electrum is a single-signature wallet which means that there's one private key for each of your addresses.

In a m of n multi-signature wallet, there are n private keys for each of your addresses and m of them are required for signing a transaction.
As I already said, Electrum 2FA wallet is a 2 of 3 multi-signature address. This means that for spending from each of your addresses, two private keys are required.

Since your private keys are derived from master private keys, two out of three master private keys are required for spending fund from your wallet.

Let's say the master private keys are MPK1, MPK2 and MPK3

MPK1 is kept is stored in the wallet file.
MPK2 is owned by trustedcoin.
Your seed phrase can generate MPK1 and MPK3.

When 2FA is enabled, you sign your transaction using private key(s) dervied from MPK1 and with entering the 2FA code, you ask trustedcoin to cosign the transaction using the private keys(s) derived from MPK2.
When 2FA is disabled, your wallet file contains MPK1 and MPK3. You have two master private keys in your wallet file and you no longer rely on trustedcoin for making transactions.

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If you want your transaction to include only 1 output, you should spend the entire balance of selected UTXOs, so that your transaction doesn't have any change.

So what I need to do is just send the maximum amount of the current multi-signature wallet to a standard wallet, right?

Yes.

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Thank you all for the detailed explanations. It's starting to make more sense now. I appreciate your patience in helping me understand the intricacies of Bitcoin transactions. You clarified the concepts, and hopefully, this will help me better understand my future Bitcoin transactions. If I have any more questions, I'll be sure to reach out. Thanks again!