Build a Multi Seller Marketplace -- 2

We need to build a multi vendor, multi category, multi country market place for consumer products. Beta will be 10 vendors, want to launch beta in 3 months, goal in 5 years is 1000+ international vendors/sellers so must be scale-able. Vendors need to individual admin panels where they can load their own items, manage their own inventory, manage their own orders and customer service on order fulfillment. Features: Standard ecommerce product listing needs: mass cvs or manual product loads, image loads, built in seo, marketing, multi channel selling and inventory management. Software/development must have access to wide range of plugins for shipping from multiple countries, fulfillment and google shopping. Main language English and USD with multi language and currency converter. Multiple price points: 2+ price levels set by vendor, triggered by customer set up data wholesale vs retail. Shipping calculation based on location of seller/vendor and buyer/customer. This includes multi country vendors so i.e. a US vendor shipping to India vs same US vendor shipping to Canada customer will need to calculate different shipping. All other basic e-commerce current features found in a hosted solution like a shopify or big commerce. Design/Navigation: There will be 3 macro categories, 12 sub categories in each and then 12+ sub categories in each of those. 10 target countries for sellers/buyers. Proposal: proposal should include software suggestion, app suggestions, other feature recommendations, time and budget/other costs to build and manage.