Buying Telegram Premium with USDT follows the same steps as buying Stars — pick the subscription instead of a Stars amount, pay with USDT on TRC-20, and Premium activates on the account.
Gifting Premium with a card usually needs the payer's own billing details on file; gifting it with USDT only needs the recipient's Telegram username.
Reusing the same USDT wallet for Premium doesn't require a new address or setup beyond what's already used for other USDT payments.
That depends on the subscription option selected at checkout, not on the payment method — check the option chosen for whether it's one-time or repeating.
If the option isn't set to repeat, yes — a new USDT payment covers the next period when it's needed.