I dunno if anyone here hasn't seen the show, but I'm glad this game got you into it! Its a weird way to get into it but it is my firmly held belief that everyone should watch Avatar at least once. Its one of the few perfect things in this world. Also, experiencing the wonderful personalities and stories of these characters might cause the slave route to put a bad taste in your mouth...
Just a piece of advice, watching Korra is entirely optional. Its a terrible show and totally fucks the canon, and the characters and story are insufferable and irritating. It has some redeeming moments, but not many.