Flip Out Screen: http://short-circuit.com
Computer: Are these things you already have laying around, if not, you can find something much more powerful for less money.
Internet: D@mn your lucky. My area is still stuck on 3G, already have a network though in the car. I used a switch connected to the ethernet port and an access point.
Accessories, you mean a touch pad and keyboard? Try this bad boy, it isnt out yet but you can preorder. http://usb.brando.com/lenovo-mini-wi...8c034d015.html
Most people go with either a M2-ATX or M4-ATX. I think you'll be fine with a M2-ATX.