WordPress backend developer

We are looking for a developer who can use ready html and make fully functional ecommerce website that has online t- shirt customization tool. You will work with website designer who have html available for all pages. The pages are done and ready for you. You have to be able to input all templates and need products taken from some other site so he will use some api to take products to your website. The main web site goal is let people upload their own design, photo, graphics or logo to a shirts, labels, decals, car wraps, etc. or they should be able to create something from our clip art/picture library, templates and fonts and we will just take care of printing production, payment and shipping. You should fulfill the site with products (synced from T-Shirt supplier library), pre-designed artwork and templates as sample website has along with functionality, payment and shipping system. Main web site functionality should be better than the samples: [login to view URL] - we think this is the best on the market as far as functionality; however we would like to have even better options as for example showing sides for sleeve printing, collar, back side, ordering different colors, sizes, designs at same time. There is a couple more functions we will need which are not included in theirs website, for example be able to order different shirt colors and sizes with same or different design in one order, but we can talk about those details later.  Other samples: [login to view URL] or [login to view URL] or www.stickeryou.com. The site needs to be build and programmed for best functionality, fast responsiveness and easy customer use, we are not interested with any cheap and limited plugins from Envato market or similar. We are getting shirts from this company [login to view URL] - (they have library to sync via api) so you will use description of shirts and other products from there but we should be able also to input different products manually. You will have a full support from SanMar integration team via email and Skype and also manual for integration. We would like to focus on digital printing only which means we would like to do smaller quantity prints and be able to ship via USPS priority flat rate programs. Again, we would like to have modern, clean, user friendly, search engine, mobile friendly & responsive, SEO friendly and optimized website. Mobile app would be optional.