The available bandwidth is a limiter, as you mentioned, but we found that the speed of the computer running iCamSource can also be a limiter. Some users with older computers need to turn off motion detection in order to get one camera working properly. On the other hand, we've heard from users that run 10 cameras on one computer without problems.
If you're talking about Wi-Fi cameras, then the camera settings will have a major effect on how many cameras you can run. You will be able to run many more cameras if they are outputting 10 frames/sec than if they are outputting 30 frames/sec. The camera's output resolution can also have an effect.