Rock Lee is depicted as a highly determined and hardworking character in the manga. He doesn't have natural talents but makes up for it with his perseverance.
Rock Lee has a sad story of constantly facing challenges due to his inability to use ninjutsu at first. He was often looked down upon by his peers. But he didn't give up. He trained extremely hard, pushing his body to the limits with his taijutsu. For example, his weights that he always carried around were a symbol of his self - imposed hardship. All he wanted was to prove himself as a great ninja in his own way.
I don't really know if the 'rock lee ghost story' is popular. It could be popular within a niche community of fans who are really into Rock Lee and also interested in ghost stories. But if it's not widely known outside of that small group, then it's not very popular in general.
A really interesting 'Naruto Rock Lee Fanfiction' is 'Lee's Hidden Potential'. In this story, Rock Lee discovers a new form of power within himself that is not related to the normal chakra system. It's a fresh take on his character, and it explores how he adapts to this new power while still staying true to his original values of hard work and perseverance.
Definitely. A lot of fanfiction writers are attracted to the dynamic between Rock Lee and Sakura. Some stories might show how Rock Lee's determination affects Sakura, or how Sakura's medical skills come in handy when Rock Lee is injured during a fight. There's a whole range of ideas that writers use to create interesting fanfictions about them.