Giving your customers a Unique code and displaying a set of products based on the code can stay outside the plugin. So you can have another script that takes this code and displays a set of products to the customers (eStore doesn’t need to know this logic).
You can specify a number for “Available Quantity” for each product and when it runs out eStore will automatically make it unavailable to buy. The main part that I don’t know how to handle is the sending of unique codes per product.