For invoicing and tax, I do everything through Google sheets. Accessible anywhere, link any cells/tab from any other one, complex formulas, it has all you need.

For invoicing and tax, I do everything through Google sheets. Accessible anywhere, link any cells/tab from any other one, complex formulas, it has all you need. For purchasing and receipt collection, I take a picture of the receipt with my phone, always on me, and put it in a folder.