Build Inventory Module on Salesforce Integrated with Xero

Hello, We want a simple Inventory Management app that is integrated with Xero. The process should work like this: - Convert Quote/Opportunity to Order in SF (Make this automated) - Make Product Quantities "On Hold" and reduce Inventory "On Hand" - Once invoice is created remove Quantities from "On Hold" - Handle RMAs (Returns). - Add "Minimum Quantity on Hand" New purchase orders received in Xero should update the inventory in SF. Quantities "On Hold" and "On Hand" should be updated back to SF. We are on the Professional Edition but we have the Web Services API enabled.