Output Excel sheet with functioning cells, and private tax withholding

Hi, lovely app! The two things that immediately jumped out at me after using this for the first month of a freelance gig:

1. The Excel file this outputs has cells that don't function, e.g. no "sum" function for the total. I'm finding I need to make an adjustment here and there and it's essentially a 'dead' spreadsheet. Perhaps I'm missing something?

2. Re tax withholdings: since I'm freelance, I'll be the one taking out my own taxes, not my client. So in this very common case, I'd be using that data for my own purposes, not to share with the client in my invoice. So it would be great if the xlxs file did NOT contain that tax withholding, but I could still have that info in the app for my own purposes.

Thanks and nice work!