Yes, there is. The 'Avatar' movie by James Cameron was also based on a story which could be considered as a novel concept. It has a rich and detailed fictional world, which was brought to life on the big screen and also has elements that could be developed into a novel.
Fanfictions have the power to expand the Avatar universe in multiple ways. Firstly, they can go deeper into the cultural aspects of the Na'vi. We got a glimpse of their culture in the movie, but fanfictions can explore it in more detail, like their mating rituals, their educational system for the young ones, and how they choose their leaders. Secondly, they can create alternate timelines. What if the RDA had a different leader who was more sympathetic to the Na'vi? This would change the whole course of events. Also, fanfictions can add new locations on Pandora. There could be hidden valleys or floating islands that hold secrets and new adventures.
One interesting Avatar fanfiction could be about a new tribe discovered in Pandora. They have unique abilities that no one has seen before. The main character, a human who has chosen to side with the Na'vi, embarks on a journey to learn about this tribe and their ways.
Definitely Jake Sully. Since he's the main character in the movie, many fanfictions revolve around him. Writers might explore his life before coming to Pandora, or his further adventures and leadership among the Na'vi after the events of the movie.
The Avatar story mainly revolves around the conflict between humans and the Na'vi on Pandora. Humans are there to mine a precious mineral called unobtanium. Jake Sully, a disabled ex - marine, gets involved in the Avatar program. Through his avatar, he starts to understand and then fight for the Na'vi against the human military's destructive plans.
It's hard to give an exact count. The number of Avatar comics by James Cameron might change over time as new ones are released or older ones become less popular. Your best bet is to do a detailed search online or check with comic book publishers.
One really creative storyline could be about a human who was born on Pandora and has to navigate between the two cultures. This character might have unique abilities due to being exposed to Pandora's environment from birth. Another could be a story that focuses on the backstory of some of the minor Na'vi characters we didn't see much in the movie. For example, exploring how a particular Na'vi came to be a part of their clan's warrior group or how they discovered a special connection with the Eywa. And then there are fanfictions that imagine a different ending to the movie, like what if the humans and the Na'vi found a more equal and harmonious co - existence right from the start instead of going through the conflict.
One interesting concept could be exploring different clans of the Na'vi that were not fully shown in the movie. For example, fanfiction might delve into their unique cultures, traditions, and how they interact with each other and the environment in ways different from what we saw in the film.
How about a crossover with Jurassic Park? Scientists from the Avatar world could visit Isla Nublar or a similar place. They might study the dinosaurs and compare them to the unique creatures on Pandora. There could be a plot where they have to work together to stop a dangerous hybrid creature created from both worlds.