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.
Well, start by planning out your story and deciding the key moments you want to show in each panel. Then, think about the flow and transition from one panel to the next to create a smooth movement.
First, you need to have a clear story or idea in mind. Then, plan out the key moments or actions for each panel. Make sure the sequence makes sense and flows smoothly.