Hi Chriojan,
I’m going to respond in two seperate posts. First RE: your question about swapping to USDT -
Correct, you can swap all your tokens on the exchange to USDT to avoid paying gas fees, keep in mind that the exchange also charge fees to swap for these tokens. After you have transferred to MetaMask, you are also correct that you can re-purchase these tokens on a decentralized exchange or swap for them on MetaMask Swaps, but also keep in mind that some of these coins may not be available to swap for if there is not enough liquidity for it. MetaMask swaps charges a small fee. Also, if you’re desire is to transfer USDT to a centralized exchange and purchase there too, you can do that too. One friendly reminder is USDT is available on several networks so being conscious of which network is always important, especially when sending or doing swaps.
Here is more information about MetaMask Swaps on the Knowledge Base if you are interested: