Best Practice for Vendor & Item tracking who are not our Vendors

We inspect products entirely at our Client's vendor locations. These vendors are reused on multiple orders and we will need the ability to see what inspectors we have assigned to work at these vendors. We must also track the fulfillment of these items that our Client purchases. Also, we may have multiple vendors and / or sub-vendors on an order. These items have no financial impact on our company. We bill strictly hours and expenses. We are interested in hearing best practice methods for establishing these vendors and items and associating them to Projects and/or Sales Orders.

We are setting up the hours and expenses to be tracked for invoicing and payment on Projects. We have been told we would need to establish Sales Orders to associate these vendors to Service Orders in the form of "items". Non-inventory items would also be attached to the Sales Order for fulfillment tracking.