"Hey, i was just wondering, and maybe would wanna try it out."
I'd feel sorry for your poor clients if you do. You dont try it out you do or you don't. What if you get fed up and think it's not worth it - they're the ones that are screwed. If it fails and becomes unsustainable be prepared to keep it going a bit til you've let everyone have a chance to move, not just hit a dead site.
First thing to know is are you prepared to put he work required in the rest of the info is easy to come by.
Study some stuff on servers/utilisation (visit the forums of things you may want to allow like BB's, Blogs, etc.), web server software, bandwidth/usage implications, available server/hosting tools, work out how much time you 'can' not want to spend each day on supporting your customers and look at tools to help you do it like messaging clients and scripts.
Should keep you going for a bit - google is probably the best tool at the moment, read at least a bit on each subject.
I'm sure some of the folks here will have some good specific links too.