Welcome to ARCHIUCAD-talk. Kudos for finding the other thread on furniture schedules, but that thread is 9 years old and a different question, so best to start a new topic in this case.
I can't totally understand what your question is - as something like furniture purchases and sales does not typically fall within the architectural side of things... But, if you group and sort by Brand, you can subtotal your sales then. Grouping/sorting is in order from left to right, so you would have to drag your schedule fields to be in the desired sort/group order.
