Can't you just add all of them for the preference of everyone and that's a good option if you're going to be with a stable coin? But if it's with USDT then I would agree with the trc20 protocol because of the fees.
AFAIK, there's also USDT for Bep20.
I think there are still some altcoins that you might be able to use because what you are looking for is very cheap transaction fees, such as TRX, which in my opinion currently still has a good chance.
I think he's going to build a casino that's focusing for with stable coins.
its a player vs player roylette and blackjack. its not exactly casino. I will just take fees from the games played and players will win each others money not mine.
It can accept all types of coins, however I was thinking about stable coins to be more easy for the players to know how much they are betting.