1. Exactly. It is often better to work from the bottom up instead of from the top down - single cells make top-down extensions select entire columns (which is bad )

2. Yes - that is how goal seek works. It requires an initial guess and then makes small changes to that guess and sees which way the end result changes.

3. The macro is assigned to the shape by right-clicking and choosing 'assign macro'. If you have existing code, that is often simpler than using the click event and calling the macro. (Really, just my preference.... I usually have the code done and tested before I add the button, and then I would need to remember what I used as the macro name!)

Lastly - thank you, but that's not needed. Just pay it forward. 30-odd years ago, a lot of great Excel users helped me, so when you get good...