His sensei, Iruka. Iruka has always been like a father figure to Naruto. He would be there with a big smile, giving Naruto words of wisdom and pride. His presence would mean a great deal to Naruto on such an important day.
His family, especially his son Boruto in the future. Boruto would look up to his father on this big day, seeing him as a great hero. And Naruto would be so happy to have his family there, sharing this moment with them.
Iruka could play a role. He was Naruto's first teacher who believed in him. He might have some small piece of information that starts Naruto on his journey to find his parents. Then there's Tsunade. As the Hokage, she has access to a lot of secret files. She could either be an obstacle, not wanting Naruto to dig too deep, or she could be a helper, providing him with crucial information. And of course, the Nine - Tailed Fox. It was sealed inside Naruto by his father, so it might have some memories or knowledge related to Naruto's parents that it could share with Naruto.
Naruto might meet his future children. He would be able to see what kind of people they are and what their dreams and aspirations are. It would be an emotional moment for him, seeing his family in the future.
Obviously Naruto himself is the most important as he's the one seeing the future. Sasuke would likely be there too, as he's Naruto's closest friend and rival. Sakura would probably also play a role, maybe as a skilled medical ninja in the future Naruto sees. Kakashi might also show up, perhaps as an elder guiding Naruto in his leadership role.
Sasuke is definitely one. Since Naruto already knows Sasuke's path in his previous life, he could change Sasuke's fate. Also, Kakashi. Naruto might interact with Kakashi differently, sharing his future knowledge which could impact Kakashi's decisions.
It's possible that Naruto would talk to the ghosts of the Uchiha clan members. Given the complex history of the Uchiha and Sasuke's importance in Naruto's life, communicating with these ghosts could help Naruto understand the clan better. He might also be able to prevent further tragedies related to the Uchiha by learning from their past mistakes.
Another character could be the Nine - Tailed Fox. Kushina was once the jinchuriki of the Nine - Tailed Fox. When Naruto meets his mother, the topic of the Nine - Tailed Fox might come up. Maybe Kushina could tell Naruto some secrets about controlling the Nine - Tailed Fox's power that she learned during her time as its jinchuriki.
Iruka sensei could play an important role. He has known Naruto since he was a child and might be able to provide some insights or memories that are relevant to Naruto's newly - revealed heritage.
Perhaps an unknown and powerful dark ninja. This ninja could be from a long - forgotten clan with dark powers. They might have a vendetta against the Leaf Village and see Naruto as the key to their revenge. So they use their dark arts to make Naruto lose his sanity and turn him against his own village.
The Nine - Tails could be considered as a 'visitor' in a way. Since Naruto is in seclusion, he has more time to interact with the Nine - Tails inside him. Also, it's possible that some of the spirits of the past Hokages might visit Naruto. They have a connection to Naruto, and they might want to guide him during this important time of self - improvement. They could share their experiences and knowledge to help Naruto become a better shinobi.
Hermione would still likely be important. Even if Harry is doing his own thing, Hermione might try to keep him in line or offer her intellectual support.