Well, a great plot could be the reincarnated Gojo trying to change the fates of his comrades from his previous life. He could use his knowledge of the future to prevent their deaths or misfortunes. Also, he might face challenges from other powerful sorcerers who are jealous of his power or suspect his true identity. This could lead to some intense battles and power struggles.
The character can start by using Gojo's charm and confidence. Since Gojo is known for his flamboyant personality, the reincarnated character can use this to make friends easily. For example, cracking jokes during dangerous situations to ease the tension among the group. They can also show their loyalty by using Gojo's power to protect others when in trouble.
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.