The distance between the JJK manga and anime isn't too significant. The anime mostly adheres to the main plotlines of the manga, but there might be some minor tweaks for the animation format.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.