The theme of friendship and mentorship also pops up a lot. Even though they are from different eras, they can still form a bond. Aang can act as a mentor to Korra, guiding her through spiritual challenges that he has already faced. And Korra can show Aang how the world has changed and how she is adapting to new threats in a different time.
To be honest, I don't have an exact figure. But you can look up on popular comic book databases or ask in comic book enthusiast communities to get a clear idea of how many The Legend of Korra comics are out there.
One great 'Aang x Korra fanfic' is 'The Avatar's Legacy'. It beautifully weaves together the different eras of Aang and Korra. The story has a great plot where they have to team up to face a new threat that combines the old and new evils in their world. The character development is on point, showing how their different personalities and experiences complement each other.
In a 'Korra meets Aang' fanfiction, a storyline could be that Korra is having trouble with her connection to the past Avatars. Aang then comes to her as a sort of mentor, guiding her through the process of strengthening that connection. They could also face a common enemy that is trying to sever the Avatar's connection to the past altogether, which would force them to fight side by side and use their combined powers and knowledge to overcome the threat.