need your help, i know someone knows this im just ignorant to what to use

pretty basic request, i have a website i want to start. i can do the site do the cart its the inventory management i having problems with.
i am selling serial numbers for a product, it's completely legit and i get the numbers from the company themselves at a discount and resell them for about 10% profit. i need a way for someone to go to my site pick the product and pay then have the serial number pulled from a database i create and emailed to them and then that number never be accessed again. on to the next number in line for the same product. don't want 2 people with same serial number for same product. i can update the database myself with new serials everyday if necessary but i don't know what to use for this database and how to do the auto email after paying for it.

if you need more details please ask, i need the help and i need to learn.

Thanks!

The Sales Guy
Dale