How do you link "assisting" staff to a specific order?
That's what part is confusing me. It doesn't really matter if it's in the Customers or Orders table really, as long as it's in one of them and I'm not sure how to relate them either.
Actually, it can matter quite a lot. How many staff might be linked to a given customer or order. Just one or many staff? If many staff, you should set up a join table for linking assisting staff to clients or orders. I'd lik to client if the same staff always assist a given client and to orders if the assisting staff may change with each order.
Staff::__pk_StaffID = Staff_Order::_fk_StaffID
Orders::__pk_OrderID = Staff_Order::_fk_StaffID
Staff_Order would be your join table.
Note that you can choose to use the join table to link all staff involved in this order not just the "assisting" staff. A field in the join table can be used to identify the "Primary Lead" (or whatever) and the "assisting" staff.
Here's a link to a demo file on many to many relationships that you may find helpful: http://www.4shared.com/file/dZ0bjclw/ManyToManywDemoWExtras.html