Build responsive eCommerce platform

I am looking for proposals from web developers who can build a shopping platform.  I would like to hear from developers who are comfortable building a shopping platform outside of Wordpress, Wix or other similar sites as the site will be hosted elsewhere. The developer will be expected to: build the platform following the designs which will be provided to the winning proposal; build a custom Admin CMS enabling me to validate new sellers and their business before  being allowed to have full access to the Seller’s platform; build a Seller’s platform to the specifications in accordance with the designs, which will also  allow Sellers to safely add their business details, upload products, necessary details and  documents for account approval;  build a buyer’s platform for customers to purchase items, create wishlists, save items and view previous orders; add a working merchant’s acquirer’s account, which also accepts Paypal as an option;and add an animated 'add to cart' function, which can be clicked to show a drop down menu of items in the cart rather than having to go the cart page. In the proposal, I expect recommendations in regard to the chosen language for backend coding (with reasoning) and a short list of merchant acquirer accounts for this project. The winning web developer will be expected to sign a NDA, web development agreement and copyright assignment.  I would like this project to be completed within four weeks; however, I am open to variation depending on the strength of the proposal. As regards price and payment, I'm looking in the region of £400.  It is also very likely that the winning developer will be called upon for other projects down the road.  Please contact me through PM if you have any questions