GOOGLE SHEETS - how to automatically display cells horizontally

This is my first time posting and I hope someone can help.

I am not sure how to word this - here is my best go...

Please see example spreadsheet

Below I explain what I am trying to achieve that corresponds to the spreadsheet:

1. Clients pay a setup fee in a certain month - (B5)
2. I identify through a formula the month that the fee occurs - (C5).
3. There is a certain number of months (B7) after the fees start to roll out based on the fee schedule (Row 3)

4. DESIRED OUTCOME (Row 12) - I would like a formula that understands that the fee is paid in Month 3, then from Month 7 will roll out the start of the fee schedule from Row 3 (starting from Month 1, automatically)

Hope this all makes sense - please let me know if I can clarify anything and very much appreciate any help.