I'm a BIG fan of the animated series, and no, I won't be watching any of the M. Night movies.
The actors playing Katara and Sokka I could live with, but the kid they picked to play Aang seriously creeps me out, and an Indian as Zuko? Oh hail no! That's just wrong on so many levels.
From the previews I've seen, the first movie looks to be Book 1, so I imagine there will be two more movies for Books 2 and 3.
I do believe Appa's in the movie (CGI), but I haven't seen anything about MoMo.
I'll just stick with rewatching the animated series and avoid the live action movies. No need to taint my enjoyment of Team Avatar.