Design and build a Content Router prototype

We are looking to build a content router prototype. It will be used in stationary and mobile environments and provide a number of simple tasks: a) stream videos up to 480p b) show a picture slide show (500 pictures) c) show various (offline) webpages d) stream music e) provide browser games (flash or html5) based Content storage should be an external SSD drive that can easily be exchanged (for updates). Internet connectivity is optional via 3G often it will have none. The box shall be light weight, shall not have a fan and even under load not exceed 100 degrees F. Eventually it should all fit into a small, very light-weight, sturdy box that allows simple change of the HD for consumers. Operating system shall be Ubuntu. No battery required we assume continuous (12v?) power is accessible. We may have up to 200 parallel users per router so performance matters (though we can specify a smaller number of users if needed). Great Wifi performance is paramount so we should have a solid external antenna. From another vworker bidder (thanks!) we have received the suggestion to base it on an embedded ARM board with SSD SATA drive. [login to view URL] It's a bit pricey but could work for us. However we are open to other hardware suggestions. We want this box to be accessible via web browser from the client. All functionality as above should be working (though it can be a very crude first version). Again it's a prototype that we use to showcase our venture, we do not expect a perfect version.