One common theme is character exploration. Fans often want to dig deeper into the psyche of the characters Edward Norton has played. For example, in fanfictions about his role in 'American History X', they might explore the process of his character's transformation and redemption in more detail.
Partially. The movie takes inspiration from real-life situations and issues but adds fictionalized aspects to create a compelling narrative. So, it's a mix of truth and creative interpretation.
One popular type of Edward Norton fanfiction might be those that explore his character from 'Fight Club'. Some fanfictions could focus on Tyler Durden's backstory in more depth, like how he came to be the way he is in the movie. You can find these on various fanfiction platforms by simply searching for 'Edward Norton Fight Club fanfiction'.
One common theme could be friendship. Given their status as well - known actors, fanfiction might explore a fictional friendship between them, perhaps set in Hollywood. Another theme could be a crossover of their movie universes, like if a character from one of Norton's movies entered the world of one of Gere's movies.
American History X is indeed based on true elements. It weaves together real societal problems and personal experiences to create a powerful narrative. However, it also incorporates fictional elements for dramatic effect and to better convey the message.