How to incorporate a 'partially paid' status for bills

This is a post mainly intended towards @Steve as he is well versed with the context which I am about to bring up again for a new requirement. For this I won’t be detailing my requirements from scratch.

Other potential solution seekers or solution providers, here are the posts which if read first will help make sense of this:

As we had incorporated a bill paid / unpaid action mechanism by using actions and select expressions, I now wish to incorporate a ‘partially paid’ status for bills that are paid. Because most of the time payments are made in round figures, which don’t amount to the total of any combination of bills, but short of a certain amount for one (lets take it this way for convenience’s sake). So I want to mark that bill partially paid.

I have a faint outline on the process:

  1. (In context with the linked post) When I add bills by their number in the company payment form, the amounts from each one add up to a total in the Total column. Now incorporating a manual ‘override’ for the amount can be the first step.

  2. The override will ask me to choose which bill I want to partially pay, and ask me to enter the amount.
    I dont know if it’s going to need another separate form for this.

  3. That amount, and the amounts from the bills that are chosen to pay in full are added up to fill the ‘total payment’ amount field.

  4. An action (like the ones markign the bills paid/unpaid) will mark the bill ‘partially paid’.

Though I have the outline, I don’t have near much idea on how to achieve this. I have learnt quite a bit in the past few weeks, and I hope I’m not going to need a lot of explaining as I probably now can pick up from little guidelines which you are always more than happy to provide.