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.
First, you need to understand their characters well. Read the original manga or watch the anime to get a sense of their personalities, powers, and relationships. Then, come up with an interesting concept. It could be something like a time - travel story where they go back in time, or a story where they have to face an enemy together that challenges their bond.
For a beginner, 'Gojo's First Adventure' is a good choice. It's easy to follow and gives a great introduction to Gojo's character. It has simple language but still manages to capture the essence of Gojo's cool and powerful nature.