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.
The ending of a novel usually referred to the climax of the novel. In a novel, the author would usually give a perfect ending to the story.
The purpose of a novel was to let the readers have a satisfactory result and at the same time give the readers a deep understanding of the story. Therefore, the plot was usually one of the most important parts of a novel.
However, the novel did not have to be finished before it could end. Sometimes, the author might leave some suspense in the novel's ending to let the readers continue to think about the ending of the story. Therefore, whether the novel's overall plot was enough or not still depended on the author's intentions.
It's hard to pinpoint exactly where Gojo is at any given time in the manga. His whereabouts change as the story progresses and different scenarios unfold. It could be in a supernatural realm, a mission site, or interacting with other characters.