Create a WordPress Template

I am trying to make a theme for my website in wordpress, that I can later sell as well on themeforest. I am thinking it like a template that allows the persons to make their own CPU online. Something similar to [login to view URL], I myself am a web developer and a designer, so I would be working in with you. Following are the features I am looking for: 1. User Cart with multiple CPU Items 2. User would pick the RAM, GPU, Processor, Motherboard etc by himself. 3. Paypal Integration 4. Accessories such as Mouse, Keyboard and others should also be made available.