Okay so the way this is gonna work is that we're going to follow the show's formatting, with different "books" and "episodes" with their own arches. We're starting with a collab post from @regitnui
(if that's what you guys agreed with) that will set the stage for us. The other characters will be introduced en route to or in Ba Sing Se (so you'll need to figure out a reason for your character to be present).
I think this is going to be pretty heavily collab-post based because it's definitely the easiest way to narrate battles and the like.