If I understand your question correctly, yes, "How many installments?" is the correct way to ask when paying for a large purchase by credit card. See below for an example.
A: Ok, that will be $1,500.00
B: Do I need to pay the entire amount up front, or can I pay in monthly installments?
A: We offer a payment plan, yes.
B: How many installments?
A: You can pay over a period of XX months, which would leave your payments at $xx.xx per month. Does that sound good?
B: Yes, that will work perfectly. Thank you.