Online Shopping Portal

We want to improve our present web portal using, Zen Cart, made by us, for our client, and replace it with a more modern Free Shopping Cart ( like Joomla Virtumart / Magento / Open cart etc. choose the one which you are most comfortable with. Technology no bar.) with 400+ products, with PayPal integration and having built in, self-sustaining, self-compliant S E O, S E M features (Google Analytics etc., properly structured, with meta data picked up from the product data). We nee the followings in the new web portal: 1. The store should be capable of being updated, always, smoothly, using a single excel/ .csv sheet, reliably without losing any data (Tomato Cart update requires you to delete all products, before uploading a new set. That solution is NOT ACCEPTABLE) and without throwing up errors. We will be doing this multiple times, later, even after the project has been completed and the full payment has been made. THIS SHOULD ALWAYS WORK. 2. A system to eliminate copy & paste, while we are printing orders- Mailing Slips/ Customs Declarations/ Invoices etc. according to the format that we provide (something like MS Word mail-merge but automatic). Not even a single copy & paste should be required, as long as the address during checkout was correct. Use connections, to the database for doing this (or any other technique you are comfortable with). A complete ready-to-print PDF being mailed to the, sales email address after order completion; is the minimum acceptable solution. Anything better is welcome as bonus. 3. It should also create daily inventory deficit list, according to daily sales made, with 12 Noon IST, as cut off time. 4. Reliable and verifiable, complete transfer of traffic from 2 separate old domains, to this one new particular one (A? New A, B? New A) 5. List of products will be provided, by us in the form of an excel sheet, to the developer with all related data (description in html, category(s), price, weight of items) and should all get updated in 1 shot so charge-per-product bids will not be entertained. Bid only if you already have good experience in building an integrated solution for Online Shopping. 6. Abandoned carts should be suitably handled with instant automatic emails directly to the customer & the seller. 7. Old users accounts, from our old Zen-Cart based website, have to be imported, to the new one that the freelancer will be now making. 8. Guest Checkout like [login to view URL] i.e. no log in required, enter email address to proceed, without log in OR log in via Google or Facebook. 9. Freelances should enlighten us, on which Free shopping cart, he is going to use, giving cogent reasons for its selection, his experience on that cart, mentioning couple of successful running web-portals, commissioned by him, for our info only and mentioning its technical advantages over the other competitive carts. 10. Support for smoothly importing products from any other web-portals, like Import Products from any e-commerce site. Finally, Freelancer shall handover the controls/ passwords and delete all data provided from our side after completion of project. Total confidentiality is expected. We might need more features implemented in the future, in a separate project, so desktop app development is an added bonus, if you want to get re-hired. If you can implement those features in a web-based environment, it is even better.