I was thinking about accepting Tether as a payment currency. But that would make it more complicated for me since in that case I would need to have wallets on all different blockchains. Also sender needs to know to which wallet to send the coins
I'm right about this?
no, you do not have to accept USDT on all blockchains, you will accept it on some, and some will not be supported
for example, USDT on Tron is a good example of efficient crypto, that do not take much for transaction, but it could cost some for Ethereum, and you do not have to accept that (although you probably will accept on Ethereum, it is a standard)