All you are seeiy on custodial wallet and exchange accounts are not actually coins, they are just numbers representing the coins but not actually coins.
The numbers represent coins that you don't have access to. Only the custodial service has and you deposited them in one of their wallets.
Unlike while using reputable noncustododial wallets, it is your coin on blockchain, only one confirmation is needed.
Good wallets will show you incoming unconfirmed transactions as well. As soon as the transaction is broadcasted by the sender, your balance should be updated with an explanation that the transaction is still unconfirmed and is waiting to be mined.