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.
One great aang and korra fanfiction is 'The Avatar's Bond'. It beautifully explores the relationship between Aang and Korra across different timelines. They face challenges together and learn from each other's experiences as Avatars.
Well, perhaps Korra could learn some of Aang's early airbending techniques. Since Aang was the first Avatar to master airbending in a long time, he might have some unique knowledge to share.
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.
It could change the way benders view the Avatar's power. Seeing two Avatars from different times interact might make them realize the vast potential and flexibility of the Avatar spirit.