B2B Online Market Place Social Networking Website Required

We want to build an online market place for selling software relating to a particular IT industry area. CMS - Content Management Frontend to add articles etc. Ecommerce system that allows developers and software vendors to sell their own software and software licenses. This software will be delivered via electronic download. Vendors of the site should be able to create their own account and add their own : profile RSS Feeds displayed on their profile so they can link to their own blogs and twitter feeds software items for sale in including the abilty to upload this software links to demo sites etc. Vendors will be notified by email when someone buys their software. We should able to search products on the site There should be a category system for different types of software solution It should be possible to find software by Developer/Vendor It should be possible to provide a link to download from another site like codeplex. Payment gateway should integrate with Paypal and Sage Pay and Google Customers of the site should be able log in and re-download their purchases at any time. Their should be a review system so software that customers have purchased cab be reviewed. Optional functionality - affiliate tracking would be useful Forum A forum should be integrated in the system so vendors and users can interact using the same login. Other social networking tools would be attractive. please detail what you can provide. Please quote estore in the reply so I know you have actually read this and aren't bidding blind. Please detail what ecommerce system etc you are proposing to use if it is an off the shelf system you are using as a basis and also what technology you will use. (PHP, .net) etc