cool, I hope this goes well for you!
I've been trying to get a feel for what maps people play and trying to incorporate it into my own server too. While i'm not expecting to ever have a 16 player game (full ctf 'siege' would be awesome though), maybe at least it'll introduce people new to the game to maps that actually have some sort of gameplay value.
Anyhow, might I suggest the following:
djw-deltastation - http://hce.halomaps.org/index.cfm?fid=221
or
fission_point - http://hce.halomaps.org/index.cfm?fid=710
These are small maps and are probably suited for maybe a 4 vs 4 ctf game (or 3 vs 3 for fission point).
Also, anyone ever played a game on this map?
Solitude (by mothergoat)
http://hce.halomaps.org/index.cfm?fid=1562
Looks interesting (minus the flying vehicles because people would just overuse them).

