Simple, Straighforward Process:
1. Create Shop Page, Including Name, Description and Photo
2. Add entry + link to main registry page (this one)
3. Inside the shop page, create products with inventory set to number desired. This can be achieved by duplicating and moving products from the main page, then updating quanitites, names, shortlinks, and descriptions as desired.
I'll give you a complete rundown of this process. It will probably take you ~20 minutes to set up each registry once you get the hang of it.