I realize it more or less depends on the clients you have but could someone give me an idea of:

1) the monthly transfer the average site uses
2) the disk space the average site uses
3) the mbps the average site uses

For number 2 above, I realize you can set the limits on the plan but how much space do sites "really" use? In other words, if someone wants a 100MB virtual site, how much of that will they actually use on the average?

Basically, what I am trying to determine is how much I can get out of a host box, how much bandwidth I need and what kind of connection will do the job.

There are so many plans out there and some of them look good on the outside but have clinchers if you exceed limits.