The schedule of finishes is the spine. Every item, its supplier, its cost, its lead time and where it goes: without one document holding all of it, the same lamp gets ordered twice and the tiles arrive short.
Procurement is the hidden workload. Forty suppliers, forty lead times and forty delivery addresses is a logistics job, and it is what actually consumes the hours a studio never manages to bill.
Margin belongs at item level. If the studio buys at trade and sells on, the record has to show what was paid and what was charged for each piece, because that is the conversation a client eventually wants to have.
Approvals need dates attached. A client who chose a colour in March and dislikes it in June is a normal event, and a dated record turns an argument into a change order.