They are likely to interact with Naruto's past self. It would be an interesting dynamic as Naruto tries to explain things to his younger self without messing up the timeline too much. And Himawari would be there, perhaps teaching her young father some of her own jutsu.
They could interact with the original founders of the ninja clans. Imagine Naruto and Himawari meeting Hashirama and Madara. They could learn about the true origins of the ninja world and how things were in the very beginning. This would also give them a chance to influence the relationship between these two important figures.
Sasuke is also a likely character they would interact with. Sasuke has always been an important part of Naruto's life. In a time - travel scenario, he could play a crucial role in helping Naruto and Himawari achieve their goals, whether it's saving the future or changing the past.
Naruto, of course. Since they are in the same team in the original story, it's very likely that Sakura will interact with Naruto. She might try to change his fate or help him in a different way. Sasuke is also a main character she'll interact with. Maybe she'll try to prevent Sasuke from going down his dark path. And Kakashi, as their teacher, will also be involved in their interactions.
Sasuke and Magneto. Both are complex characters with a bit of a dark side. They could either become enemies as their goals might clash. Sasuke is on a journey to gain power for revenge, and Magneto wants to protect mutants but sometimes uses extreme methods. Or they could form an unlikely alliance, learning from each other's determination and power - seeking motives.
Naruto and Dawn are the obvious ones. Since it's a 'naruto x dawn pokemon fanfiction', they would likely be at the center of the interactions. They could start off as strangers and gradually learn about each other's worlds.
Naruto and Rey would be likely to interact. Naruto's positive and determined nature would complement Rey's own strong will. They could exchange knowledge about their respective powers, with Naruto showing Rey how to control her chakra (if she had it) and Rey teaching Naruto about the Force.
Naruto and Hiro are likely to interact. Naruto's enthusiasm and Hiro's intelligence would create an interesting dynamic. They could both inspire each other in different ways, like Naruto inspiring Hiro to be more bold and Hiro teaching Naruto about science and technology.
Kakashi could also play a role. He has been Naruto's mentor for a long time. So, he might have some mixed feelings about Itachi adopting Naruto. He could be suspicious of Itachi's motives at first but then gradually come to understand Itachi's positive influence on Naruto. Their interactions could be really fun to read about, especially when Kakashi tries to give Itachi some advice on how to handle Naruto's wild nature.
Obviously, Nagato himself would be the main character interacting with Naruto. He would be like a mentor or a guardian figure in Naruto's life.
Anko might also be involved in the story. She has her own unique relationship with Yugao and could potentially interact with Naruto. Maybe she gives Naruto some tough love or challenges him in a way that Yugao's teaching methods don't cover. And of course, Iruka sensei could also show up to check on Naruto's progress and have some interactions with both Naruto and Yugao.
Sasuke would be a likely character to interact with Naruto as a Time Lord. Their complex relationship in the original Naruto series would add an extra layer of drama in a time - traveling scenario. Another could be Kakashi. His wisdom and experience would make for interesting conversations with Naruto, especially when Naruto has the power of a Time Lord. And of course, Jiraiya. Given his close relationship with Naruto and his own adventurous spirit, he'd be very involved in Naruto's time - traveling adventures.
Definitely Shikamaru's friends like Choji. Naruto in Shikamaru's body would still have that bond with Choji, but it would be different. They might have conversations about food and friendship in a new light. Also, Ino would be a major character to interact with. Their relationship could change as Naruto is now in Shikamaru's body.