To be fair, Avatar (godawful movie aside) is one of the greats; I don't think it's at all unusual for it to attract this much interest. Personally speaking, I've been (re)reading a lot of Avatar stuff recently - Vathara's [i][url=http://tvtropes.org/pmwiki/pmwiki.php/FanFic/Embers]Embers[/url][/i] is a 700k doorstopper, but [i]well[/i] worth the read; I come back to it every few months - which is why I jumped on this so quickly, but I'd have been interested even if I hadn't.

You could ask for character submissions and then pick the ones you like most, if you want to whittle it down a bit.