Customize PHP Auction Script and Add Multi-Vendor Functionality

We currently have PHP auction script and need to change the look and add some functionality to include a multi vendor marketplace and shopping cart. Theme Change 1. Install new, responsive front end theme and back end them to change look. Compatible themes to be suggested by freelancer. Functionality 1. Redesign my account area similar to [login to view URL] and amazon.com. 2. Redesign the sell format to allow sellers to list products in auction and catalog listing format. Auction format functionality already exists. Need to allow seller to manage product catalog, promotions and inventory similar to store management (multi vendor type functionality). 3. Allow sellers to fully manage and process orders without admin involvement for items listed in catalog format. 4. Redesign the seller store layout. Allow buyers to search within a seller store. 5. Add shopping cart for buyers to checkout from multiple vendors (checkout one at a time for each vendor based on vendor payment preferences) 6. Allow sellers to bulk upload products in csv file 7. Add buyer/seller chat functionality. 8. Allow admin to invoice seller for selling related fees and seller to view invoice in my account. 9. Redesign the backend to allow easy view of site functions. Allow admin to create sub admin users and designate roles and functions. 10. Update user registration page 11. Install SSL certificate 12. Transfer domain to active site.