Naruto has been through a lot in his own time, so he may use that experience to adapt to the past. He might start by making friends with the younger versions of people he knows. He'll also have to be careful not to reveal too much about the future to avoid disrupting the timeline. He could use his ninja skills to earn respect and find his place in the past world.
Regarding his relationship with the village elders, Naruto might be able to influence them more. As a retired ninja who has seen the future of the village, he could persuade them to make different decisions, like being more open - minded about new techniques or more inclusive towards certain clans. This would reshape the power dynamics and relationships within the village.
Boruto might be in awe. He has always known his father as the Hokage, a powerful and respected figure. Seeing Naruto's past full of struggles, loneliness, and determination would make him realize how far his father has come. It could also make Boruto more empathetic towards Naruto and perhaps inspire him to be more like his father in some ways.
I'm not entirely sure specifically what this 'sins of the past naruto fanfic' is about without reading it. However, generally in Naruto, there are a lot of events in the past like the Uchiha clan massacre. It could be that this fanfic is centered around such major past events and the sins associated with them, like how Itachi's actions, which were considered a 'sin' by some in the context of killing his clan, are explored further.
Probably his time at the Ninja Academy. Naruto was always getting into trouble there, but it was also where he made some of his first friends. Also, his encounters with the Third Hokage could be shown. The Third Hokage was like a grandfather figure to Naruto, and their interactions were important in Naruto's development.
He could also develop a deeper understanding of the history and roots of the Hidden Leaf. By being in the past, he gets to experience the events that shaped the village first - hand. This makes him more empathetic towards the founders and previous generations, and he might bring back a new sense of pride and respect for the village's heritage when he returns to his own time. Well, in some fanfictions, he might also struggle with the idea of changing the past too much. He has to balance his desire to make things better with the potential consequences of altering history, which adds a layer of moral complexity to his character development.
One potential ally could be the younger versions of his existing friends like Sasuke. Even though Sasuke in the past may not be as developed as in Naruto's original timeline, Naruto could still see the potential in him and form an alliance early on.
Naruto's character might develop a greater sense of responsibility as he realizes the impact of his actions in the past on the future. He may become more patient, knowing that he has to tread carefully to avoid major disruptions.
He could change a lot of things. Maybe he would prevent some tragedies that happened in the original story. For example, he might be able to save some characters who died. He could also use his knowledge from the future to make the ninja world a better place earlier, like teaching new jutsu to the younger versions of his friends.
A great 'Naruto from the past' fanfiction could involve Naruto going back to the time when the Nine - Tailed Fox first attacked the village. He might use his connection with the fox to stop the attack or at least minimize the destruction, and in the process, change how the villagers view him and his family.