Thanks for the useful replies. I looked at the USB host, Ethernet, and Wifi Shields, and I have a better idea of how to proceed.
If you're new to Arduino, don't try to design a new product that will work for each and every person in the the world as a first project.
Start by building something simple but fun that you can learn from instead.
Don't worry, I'm not new to embedded systems, or even AVRs, just to Arduinos. 