Transaction fees and rental calculations

[querli]

Hello, I am currently having problems sending transactions. I have read the test case in the example, but there are still questions:
1, the transaction fee is composed of several parts, see the document is charged according to the signature, a signature is charged a fixed 5000 lamport, or according to the byte charge? I see that the transaction SOL coin is charged a fixed 0.000005 SOL, but I don't know what the fee is for trading tokens.
2, the transaction into the token, first determine whether the user has an account, there is no need to create and pay fees, how to calculate and charge this fee?
3. How to determine whether the balance of SOL is enough to pay the transaction fee when the transaction is transferred to token?