VA01 creates a sales order for a customer. The order captures the sold-to party, requested material, quantity and selling price. It starts the document flow, but it doesn't itself reduce inventory or post the customer's receivable. Those effects belong to goods issue and billing. Keeping the stages separate makes later exceptions easier to explain.
Use a partner with customer roles. A supplier key doesn't become a customer simply because its record has a company code. A billing block is a document control: the order can exist while billing is held for review. Read whether the task asks for that block. The exercises check the customer and item fields separately, so a correct order value with the wrong customer won't pass.