Multi-Vendor Shopping Cart for digital downloads

Hi, I am interested in having a website that will sell digital downloads like software, templates, ebooks, music, pictures, manuals, etc. Some of the requirements that are needed are below (but not only). It’s basically a shopping cart, which I also need to be taught on how to use it (please don't come up with one of those cheap imitation scripts). Multi Vendors Affiliates for vendors Product and category management Unlimited products posted 5 photos for each product (with enlarge) Uploading of any digital file Auto-download after payment Several payment options including Paypal, 2Checkout, World pay, credit cards, etc Auto emails One page checkout Site search Website optimization Etc ….. SEO friendly In another words, just to make it easier to understand, I need something like: [login to view URL] [login to view URL] [login to view URL] etc. If you study those websites, you will understand what I want. It would be good to have it in at least 3 – 4 languages (the basic ones) You should understand that I am not very computer literate, and that’s the impression we should have for the people that will be using the actual website. Yes, there are lots of shopping carts that will do the job but as I don’t have the know-how, I will need someone to prepare it for me. I will also need to know how much support I will have after operation of the website. Payment will be made after completion. Please let me know of the cost, duration till finished and which cart is to be used so that I can have a bit of look. Thank you.