IRC does sound like an existing wheel.

If I were you, I wouldn't worry about supporting a thousand users right away, just like I wouldn't worry about handling 50 hits per second on a new web site. Since this is a learning tool, do it in the language you know best (or want to learn most). Do it correctly, and then worry about doing it quickly. I'd be very surprised if Perl couldn't handle that bandwidth, given how much mod_perl can serve on a moderate box.

You might also find POE useful.