Do you have a reference set for Microsoft Excel???
What is the format for the output to be sent to tax lawyer?
You do not necessarily have to use Excel to get csv output.(as has been said)
You may get more focused help if you provided some test data.
You will also help yourself by creating a conceptual model of the business to show where and how
billing , purchase, inventory, production, and payment tracking fit together.
It's analogous to building an airplane or shopping centre --you do some general analysis to identify basic requirements. You find that some pieces will have to conform to some dimensions or weight or location in order to fit together. You end up with a developer's conceptual view of the product; and as you get to more detail, you may have to revise some things, but you do so from a point of knowledge --NOT discovering that wings or a third storey are required after the fuselage (or second level parking lot) has been fabricated.
Good luck.