Opencart multi-sellers e-commerce system changes

(before you read the project details this job requires an experience with opencart and an expert php programer please post your opencart projects before you post your bid) we are working on a multi-sellers opencart e-commerce system. the system allows sellers to create their own accounts and post their products to the website. the system gives the sellers options like posting a products and the product details. payment transactions. notifications. the opencart system is currently live here: [login to view URL] you can create a seller and learn how to the system works. we need to do the fallowing customization on the system: Seller delivery choice: - Self delivery (the seller will deliver the product to the customer directly) - choose a delivery company (Each has a cost) ( the system already have something like that) Seller payment choice (and also work out the calculation of the system billing): - PayPal - VISA payment option - Gulf direct debit payment option - Cash on delivery option (requires prepaid credit each sell will take from seller credit) Product picture upload (private - public choice): - Public choice will be the default opencart picture library - Private will upload the pictures to the seller pictures folder (this needs to be added to the system) Regards,