Well, a cool plot could involve Korra having to deal with a strange phenomenon that is causing all the bending elements to mix uncontrollably. This forces her to find a way to restore the balance not just between the four nations but also within the very essence of bending. She might also encounter a mysterious figure from the past who has some secrets about the origin of bending that could help her in this task. And perhaps there could be a sub - plot where her relationships with her friends and family are strained because of the chaos this situation brings.
To create engaging characters in a 'Be the Leaf Legend of Korra Fanfic', give them distinct personalities. For example, a non - bender character who is extremely brave and uses his wits to outsmart benders. Also, make their backstories interesting. Maybe a character was once a bender but lost their ability and is now on a quest to get it back.
The Legend of Korra comics are definitely worth a read. They capture the essence of the franchise and bring fresh perspectives. The quality of the storytelling and the visuals make them a great addition to the series.
The 'lemon' aspect might be a bit hard to come by in a clean way as it often involves inappropriate content. But for normal Korra and Mako fanfictions, you could also try FanFiction.net. Some stories there might show their relationship developing, their adventures together, and how they support each other, which can be really interesting to read.
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.