If formula that will work for multiple scenarios

Good Evening,

I'm trying to build an If formula that will work in multiple scenarios. My goal is to change the numbers in Column B and the formulas work for any and all scenarios.

Here are the main points/rules I'm trying to fit in this spreadsheet.

Cell B8 has the monthly spend while B3-B5 have funding sources. Basically I want to know when the funding sources will expire/exhaust funds. When funding 1 is out, the formula would go to funding 2 for the different in that month and so on. Once a funding source hit $0, it should go to the next funding source and so on.

I've attached the spreadsheet. Thanks in advance! Book1.xlsx

I've restructured it into a format that's close to what I usually do. Basically splitting out the "paid" amount and the "remaining balance" left overs using a series of MINs. See attached.

Awesome Thanks!