FileChucker is a great drop-in solution for file uploads, and worth every penny of its very reasonable cost. Encodable's support is excellent to boot.
Do you know how rare it is to have a "canned" shopping cart with the ability to fairly easily do complex pricing options on a single item? Maybe you do, but if you don't... basically, they don't exist! I have looked. Everywhere! And the few that might even come close to the functionality that you have in CornerStore cost a fortune!
The work, the thought and the organization you put into this app is incredible.