can i pay more than the minimum payment on the installment plan

Yes, you can pay more than the minimum monthly installment amount.

Installment balance will reduce the overall number of payments but are still scheduled to pay your future installments the following months.

You may pay off the entire balance off early if you wish but interest rate is still 0%.

Yes. See the "Pay extra" section in How to view and pay Apple Card Monthly Installments - Apple Support