When it comes to imposing a bandwidth allotment per-user... like most things when it comes to computers, either it will be easy or it will be impossible.
If you can plug directly into the router and access the control panel (enter home IP and then log in as the administrator, usually) there might be an option for limiting per-user bandwidth. With some routers it allows you to express the limit as a percentage, which is handy because the fewer users you have, the more bandwidth each one gets. Others only allow you to set the limit in kbps, and you'll just need to experiment a little to find out how much your users need to access the web and e-mail reasonably fast, without allowing big honkin' downloads.
The webcam idea is a good one, too. I don't know if you've spent much time looking at them, but I've been doing some research on the subject because I'd kind of like to install one with my weather station. There are models available now that have their own internal software, so you just plug them into your router and they make the photos available online without you having to fart around with all that auto-FTP nonsense. They're a little more expensive, but probably worth the extra money in terms of headaches saved.