You’re looking for a solution for a different issue.
You are selling for example 100 laptops. They are exactly the same, but you want to know which specific laptop is ordered.
What you basically need to do:
What is your exact question?
When I read the lines, you have almost said everything you want to do.
Creating auto-generated ID is as easy as setting the OrderID as Autonumber.
If you want to have Alpha-numeric, you can use RandomString in CommunityCommons