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.
Some fanfictions might include Uraraka's family members. Her parents could be involved in their married life, for example, giving Ochako traditional family advice. Also, Izuku's mother could be a prominent character, sharing her own experiences of being a single mother and now seeing her son happily married.
One great Deku and Ochako fanfiction is 'The Path to Heroes'. It beautifully portrays their relationship development. Another good one is 'Deku and Ochako: Training Days' which focuses on their training together and how it deepens their bond.