Custom tees or t's, flash based-2

We want to custom make t-shirts and some other products like hoodies, full face t-shirts, full face hoodies, zip hoodies, baseball caps, badges etc... for our non-profit org to make $. The Project: We need an application for our new site, and installed into opencart. It's under construction. We saw the Spreadshirt site ([login to view URL]) but it's the only one we've seen. It's close but lacks a key component, EL Panels. Copy it and its functions if you wish, modify it to make it appear to be ours by adding what makes ours different. (I've attached a pic of what we are aiming to have). Our site, [login to view URL] is OpenCart 1.5.2.1. We want the application to integrate with our site. Customers sign in to use the application, choose product, size, colour, design, upload a design and to write text; and pick EL Panels. I will supply a couple of xls file of related designs, however the images are not animated (gifs) and need to be at some point. When someone chooses a design, pays for it, we send the order to someone else for fulfillment. (big image / eps) for printing. We want the application to be dynamic. We must be to modify the source code, to add style images and inventory items and upload new designs and new products etc, so we must be provided the entire code that way if it ever needs changes that we can either do it or hire again without concern that the code is lost. No prepayment permitted (our laws do not permit us to do that).