ETH required for EXCHANGE one crypto for another ? Gas fee noobie questions

Been suing my trezor for a while without problems. Receiving, sending, converting crypto.

But I didn’t know much what I was doing, using the default.

To Exchange one crypto, I mostly use one of the Trezor suite suggestion : " changenow " and it’s working well.

My questions :

  • GAS FEE : should I leave the default (Normal) when exchanging crypto for USDC and the opposite ? If not, what is the best value for noobie

  • ETH : Am I right sayint that when converting some crypto to USDC or the Opposite, I need to have some ETH in my wallet ? I didn’t pay attention and my ETH wallet went down and down and down convering LRC to USDC or the opposite and at some point, I could not use " changenow " anymore, had to send some ETH to my Trezor ETH wallet address for Trezor suite Exchange feature to work…

Any comments or suggestions are welcome…

And presently I have transactions pending and I don’t why. If I try to BUMP fee I see Not enough funds but there is 50$ in my Trezor Eth Wallet