There are a couple pieces of information I would like to be able to add and save. I know how to add when i am the check out point (customer is standing there and I am about to sell them their computer)

Mainly is what I posted in my other question, the serial or serials of the computers but would it be best to have that here OR somehow (I don't know how how) have each computer have a field that is its serial number and then when I go to sell it I somehow select that serial number?

Is it possible and difficult to have an item like a macbook where I have 15 of them in inventory, each macbook I would have put its serial number in when I put it in to inventory. When the item is sold I want to make sure I somehow have the correct serial put on that sale and removed from inventory