Do I have to set suppliers up before raising a PO?
It is worth it. A purchase order can carry a supplier name directly, but a proper supplier record means the account number, terms and address are reused rather than retyped, and spend per merchant becomes answerable.
Can I see what I spend with each merchant?
Yes — because purchase orders, delivery notes and expenses all reference the supplier record, spend can be attributed per supplier rather than sitting as undifferentiated materials cost.
What are payment terms used for?
They tell you when committed spend actually becomes cash out. Combined with Gaffer's cash-flow forecast, terms are the difference between knowing what you owe and knowing when you owe it.
Can I deactivate a supplier without losing history?
Yes. Suppliers carry an active flag, so a merchant you no longer use drops out of selection lists while its historic purchase orders and expenses stay intact.