|The network is going to be the bottle-neck, if your uplink is limited then requests will drop. |
Your router should queue them as far as it's capable, but the ISP will drop packets if they're sent too fast. TCP retransmits, but if the retransmission is not handled in a timely manner, then the connection drops.
To get an idea of how much bandwidth you'll need, figure how many kbytes a single, normal 'session' on your site would consume, and over how long (a normal person, clicking/reading), then multiply by how many sessions you expect & add a little for overhead.
and of course set up caching / memcaching / gzipping where available & minimize the amount of bandwidth you're using.