Build a stock inventory management system integrated with OpenCart, Amazon, eBay and Play.com

We require an all in one system to manage our daily orders. We require a system that can, at our request, connect to our own OpenCart website and our Amazon, eBay and [login to view URL] account, to download and display our orders in one easy to view and manage interface. You must have a knowledge and ability to understand API's from Amazon, eBay and [login to view URL] The system must have 4 pages: Inventory Management: This page does not need to communicate wtih either OpenCart, Amazon, eBay and [login to view URL] as it will be used for our reference only. It should allow us to add our full inventory, with columns for Name, Description, SKU, OpenCart Quantity, Amazon Quantity, eBay Quantity, [login to view URL] Quantity, Wholesale Quantity and Backup quantity. It should be easy to search and fast to update quantities without requiring multiple pages to be edited. Order Page: This page must download and display all orders that have yet to be shipped from OpenCart, Amazon, eBay and Play.com. There must be an option to print all of these orders. The orders must print in the form of a packing sheet for each order. We will provide a layout design for you to work off for the packing sheet. Once orders are printed their status should change on our system to "Fulfillment" and be moved from the order page to the picking page. Picking Page: This page must display all orders that have already been printed. We must then have the ability to open and view each order. Each order should download the SKU from OpenCart, Amazon, eBay and [login to view URL] and have a text box to allow us to scan the SKU at our location with a barcode scanner. Once the SKU has been scanned, it should turn green on our system so that we can track which items are missing from the order. There must be an "Order Complete" button that will then move the order from the picking page to the completed page. It must also update either OpenCart, Amazon, eBay or PayPal accordingly to mark the order as dispatched. Completed Orders Page: This page must display all orders that have completed the previous steps and serve only as a reference for us. We will provide more detailed requirements as the project is completed. We require ongoing support and modification for at least 2 weeks after the project is completed to ensure the system works as we require.