So I could see it going a few different ways:
1) Aang teachers people who have bending talent and are interested in Airbending.
2) Aang bends the energy within some people to become Airbenders.
3) A colony of Air Nomads is found who had set themselves above even those who lived in the Air Temples, living solely in the clouds and air, undisturbed by anyone or anything below.
4) Among the many exiles are the former Air Kingdom stock, who eked out quiet lives on the fringe and disabused anyone with bending talent from learning, for fear of what would happen to them.

As for Ozai, well… you have to have an iconic villain so ungodly bad that everyone fears even their name. To scratch the surface a little means marring the perfect veneer of Evil and in some way makes the more human, and thus weak. Pacing wise, it all depended on Zuko, who is the only one who knows Ozai personally (the rest of the world only knows him as a monster; if the audience gets a feel for Ozai before the characters do, it doesn’t work). We have to follow Zuko through his progression of still wishing to please his father and revering Ozai as his lord and master, through Zuko’s questioning of his “destiny” and thus what his father represents, and then realizing through flashbacks what sort of person Ozai really is. Once Zuko accepts his father as the enemy and sides with the Avatar, the veil finally falls and we’re allowed see Ozai for the sort of human being he is.

At least, that’s my take on it.

Zuko did not have the ease of firebending that Azula did, and he was of a different mind than Azula and his father: he cared about those under him, but he still had the determination to speak his mind, which is what got him exiled. Thankfully, Zuko had repeated failures and his devoted uncle to show him that Ozai and Azula’s ways were not worth following.

What undid Azula at the very end was Ozai’s casual rejection of her. He used her for how to defeat Ba Sing Se and then tossed her aside just like everyone else he stepped on to get what he wanted. To be denied recognition by her father, around whom her entire world revolved, on the moment of his triumph that she had worked tirelessly for, was shattering. Without that, Azula found herself alone. She had driven away her friends, leaving her with no one to help her handle the rejection. So she descended into paranoia, suspecting everyone of turning away from her.

Which, to me, is one of the real messages of the story: the importance of family to keeping you grounded, helping you cope with failure, and cheering you on to success. All of the successful characters in the story had family. Katara and Soka had each other (and then their father). Aang had everyone in the group. Zuko had Iroh. Even Toph came around to appreciating her family and recogizing the strength in being part of a team.

Whereas Ozai and Azula are the epitomes of what happens when you put yourself before family and friends. Neither one cared for those who loved and supported them. They ended up being undone by those who did.