can I pay my billing incrementally before it’s due date, or do I have to pay it all on the due date? For example, if I have $200 due and I have 4 weeks, can I pay $50 a week until it’s due to minimise the cost on the due date?
Yes, you can do this even if you don't have a bill due, your account just goes into credit and when the bill is issued, the charges eat into the credit on the account.
Only thing to be careful of is depending on how you pay and your plan, there can be fee's for paying (like credit card processing fee etc). I'd double check that first to be safe