i don't think OP is planning to convert his assets into USDT. perhaps he's planning to convert some into USDT to facilitate trading processes. USDT is easier to send/transfer and is a preferred currency over USD in most exchanges. USDT has been for many years and won't likely to collapse in an instant. nevertheless, never put in more than you can afford to lose.
Well in this case, if OP isn't planning on holding the USDT for a decent time but probably just to quickly move funds over exchanges, then getting a wallet is probably a waste of time. Simply just move the funds from exchange<->exchange.
Having a cold wallet for storing the cryptocurrencies and hot wallet for moving coins between exchanges is necessary in my opinion. If OP wants to transfer high amounts, using wallet is desirable for preventing possible security issues.