OP, as I'm sure you know, monthly payments can only be paid by direct debit from a US bank checking account. In case you aren't aware, you can pay off all or part of the balance with a credit card (to get reward points), or with Disney VISA reward points, or with Disney gift cards, or of course with a check, at any point during the year.
I have a couple of annual bills due in January so to manage my cash flow, I signed up for monthly payments for my DVC dues. I let the January and February payment get paid by direct debit. In March or so, I buy discounted Disney gift cards and use those plus my Disney VISA reward points to pay off some or all of the balance.
Just be aware that if you pay off part of the balance and you own only one contract, your monthly payments continue at the same dollar amount. In other words, they don't recalculate your payments based on the remaining balance and the number of months left in the year. They continue to debit the same amount and you end up paying off the balance earlier in the year.
If you own more than one contract and you pay off part of your total dues balance, they apply the payment to each contract in turn. Say you had three contracts, they would apply the payment first to the contract with the lowest dues balance. If your payment is sufficient to pay off that contract's dues in full, they apply the rest of your payment towards the second lowest balance and so on. Say you paid off the dues for Contract #1 in full and part of the dues for Contract #2. Your monthly payment would drop because you are making dues payments only on two contracts now. Once Contract #2's dues are fully paid, the payment would drop again because you are paying dues only on the third contract.
ETA: The info above is probably out of date since you can now make payments with credit/gift cards online. The system may allocate payments differently than Member Services does. But the relevant point still holds -- you can sign up for monthly debits but make additional payments towards your balance throughout the year.