Creating a downloadable product with opencart

I am putting up an OpenCart Shopping Cart selling electronic codes. I need a developer to do these simple things for me: 1. Install the shopping cart 2. Create an electronic pin generator that can generate unique ePINS and store to the OpenCart database. I should be able to create PINS for various electronic products. Ex 100 pins for product X 200 pins for product Y 300 pins for product Z 3. Once a registered customer or buyer's order is marked as paid, the electronic PINS purchased by the customer and other product details should become downloadable and at the same time, displayed to the customer's account as inventories. 4. When the customer wants to use the product, he just clicks the product and the system should display a "USE" button beside it (can select one or multiple products). This button is connected to an API which I will provide. 5. When used (API Response), the product PINs should be tagged as "used" and no longer be usable but can still be viewable. Developer should provide me the complete working demo. I will pay through GAF only and release it once I have alredy installed it on my own server. Max budget is $ 20.00.