I think one room would be fine. I dont see need to have various rooms unless people want to discuss different topics, its moreover a general chat.
As for Moderators (called "Ops" or "Operators" in IRC) I dont think we need to worry about that unless it becomes an issue.
Chances are, a bot will be put in place with a few presets such as, kick on flooding or excessive language.
How about trying out a shoutbox?
Shoutbox is moreover a Comment system, and isnt exactly live chat.
You might be wondering why we are steering towards IRC:
One major reason is that people can use their own clients, and therefor, it can be run in a separate program, or in a web interface.
The only problem with IRC, specifically if you are using an advanced client, is that quite a bit of it is command line based. However, if a modification were to be installed for the forum, then the forum would greatly assist with the login process.
Most services like Blitzed.org and Freenode have an excellent uptime, and are fairly simple to operate. It would be more complicated for a few CH Members to make our own IRC network to host the CH Chat off of, but, it could be worthwhile. We are still looking into this as a possible option (however, it wouldent be hosted on ComputerHope's servers, since most web server hosts do not allow IRC Servers to be run due to resource restrictions. Basically: We need an expert before we can consider using our own servers.)