This is not simple question we can easily answer. This is decided by your system capacity, whether involve media processing, stream resolution and bitrate, etc. What's your scenario?
If I have quality server and bandwidth, and would need no media processing, just streams forwarding. For instance 640x480 streams. To be viewed by 100+ people. Is it possible?
I think it works if the server is greater than 8 logic cores. The theoretical capacity should be beyond this. Let us know if you can't achieve the goal.