You can try to make a prototype to lower down risk with limiting your goal to about 50 people simultaneously online. Then think about how to scale it up in later versions.
I found some points to address in the last discussions:
1. C2 MP uses webrtc, which might be blocked by some firewall.
2. You will need more knowledge about how to make a network game before you going from arcade/console games to network game.
Here is one book of my favorite (written in Japanese, Chinese version is also available)
http://www.amazon.co.jp/%E4%B8%AD%E5%B6 ... B0050QL3S2
3. Anyways, a 50 to 100 player would be a good starting point.