[Floris]

taffy: pjirc applet would allow a permission list of rooms, but I am not certain about mibbit. Worth looking into.

Not sure what you mean with usergroup lines. but .. the channels on vbirc network can have regular users, voiced users, halfops, auto ops, super ops and a founder. They each show a bit different, depending on this flag.

You can have basically unlimited amount of rooms on the vbirc network. Pending nobody else registered the room before you. First come, first go basis.

1 channel = 1 room.

Once a user is in 1 room, they can type: /join #anotherroom to go to 'anotherroom'.
Each room shows as a 'tab' in the 1 mibbit that's loaded.

Yes, the vbirc network uses about 10 servers, and currently supports up to almost 3800 concurrent users without causing network lag. We can extend this with batches of 1024 easily. That's something the network manages, and the channel owners don't have to think about this. At the moment every server is a completely different server, at a different data center, at a different data provider, at a different continent. So if 1 network has connection issues (broken switch or router) the other 9 stay online.
We currently hard-limit a channel to 1024, but we do offer the flag +L for a channel to Link a room to another room if a limit is reached. If we get a popular channel that needs 4096 users in it, we can change our network hard limit to 4096.

50 users is not a problem, at all.

Using the network we have one or more hubs, and leaf servers connecting, so if there's a load issue it's spread over all the servers. The main "irc.vbirc.com" actually has round robin dns, all the hubs and leafs are added to the pool. So if you go to irc.vbirc.com you end up on a server with least network load and lag. Allowing a quick and smooth experience.
To avoid firewall, nat and other issues we do not require identd to be running, and some of our servers even support port 8080, bypassing most work firewalls. (we have 6665-6669,7000,8000,8076,8080,9000,9999 and 6697 for ssl.

The vbirc network supports IPv4 , IPv6 , SSL , Multiple hubs , Multiple Leafs , quick connect , ChanServ and NickServ and HostServ , we auto set +x so users are 'anonymous' as their host is masked, and registered users can get a fake virtual host. We allow users to use clones, bots, and register multiple nicks and group them, and have multiple channels. And have idle or active, or very busy channels. As long as there's no racism, kiddie porn, or warez channels, we are pretty much fine with it all.