There was a thread on this a while back:
http://forums.sjgames.com/showthread...ight=airbender
As for TL, in Airbender the Fire Nation seemed to have some TL 5 (even a little bit of 6 if you count the tanks) tech but used bending for combustion so maybe TL 4+1, but the other nations seemed more solidly TL 4. In Korra, Republic City seems to be TL 6 without the need for bending. No guns for anyone still, but odd electric weapons, right? Been a while since I watched.