When should I pay the seat acceptance fee if I'm not interested in the seat given in the first round and waiting for other rounds?

Wait for the higher rounds. Paying your fees is not mandatory initially, only the registration amount is paid. After you get the college of your wish, pay the fees.

No, you should not be paying fees right away. Wait for the other rounds if you have the chances of getting a better seat according to your rank and merit. After the last round, confirm your seat and pay the fees If you do not want to wait till the last round, you have to pay the fees when you freeze