Use Apple balance first?

Apple Account balance is always used first, before any other payment method.

However, if the existing payment methods stop being verified or had an issue, it will request you verify them correctly before using the account balance. It won't charge them once they have been verified though.

If your payment methods tend to become unverified for lack of funds, then you may be better off removing them, once they have been successfully verified once.

Apple ID Account is always used first before any other payment method. Credit, debit cards and Apple Cash can be moved into any order you want. The payment method at the top of the list is always first source, then Apple works down the list. Order is adjusted by tapping/holding and then moving into the desired order.