I'm assuming we're only talking miner's fee here. 2FA fee to Trusted Coin will not grow and doesn't depend on how many transactions I have...right? (I just get charged for every 20th outgoing transaction, regardless of it's size in KB, regardless of wallet type etc)...right?
Right.
Could you estimate by how much?
Use any transaction fee calculator/estimator like:
https://jlopp.github.io/bitcoin-transaction-size-calculator/In that tool:
Set the 'Input script type' as "
P2WSH", 'Signatures per input' to "
2" and 'Pubkeys per input' to "
3" so it would match Electrum's 2FA wallet script type.
Set your number of input(
s), 4 or 20.
Then, set the output to 1 for max send; use 'P2WPKH' outputs if you're sending to a native SegWit address.