How to enter and track customer-received purchase orders

I'm using Quickbooks for Mac desktop 2015, even though the "select your product" section above won't let me choose that. I double checked, and that's what I've got.

I provide metal polishing services to my customers. I will often receive a purchase order from a customer for several hundred various parts, say 75 aluminum adapters with a certain item number, 300 steel rods with another item number, and so on. I complete these parts in batches, and return them to the customer as they are completed. What I would like to do is:

1. Input the purchase order along with the part numbers, descriptions, and quantities into Quickbooks.

2. Create invoices for partial shipments based off of a purchase order.

3. Have my inventory for those item numbers update as I cut invoices.

Maybe I'm just being obtuse, but I can't for the life of me figure out how to do this, and I haven't had any luck finding the answer in the community either. Any help would be greatly appreciated! 

Thanks! :-)