Obviously, Kakashi is one of the main characters since it's about his time travel. Minato is also a central figure as he is part of Team Minato that Kakashi travels back to be with. And of course, the other members of Team Minato like Obito and Rin are likely to be important characters as well.
A really cool plot might be that Kakashi time travels and discovers a hidden conspiracy in the past that was related to Team Minato. He then has to work with his past comrades, including Minato, to uncover the truth and prevent a great disaster that he knew about from his own time.
One good plot could be Kakashi going back in time and using his future knowledge to prevent the death of his comrades in Team Minato. For example, he might be able to stop Obito from getting crushed in that rockslide. Another plot could involve him trying to change the course of the war by influencing key decisions made by his team. He could also go back and try to train himself better in the past, using the skills he's learned in the future.
Kakashi's abilities would likely be enhanced in the past. He has all the knowledge and skills he's gained in the future. So, his combat skills would be more refined. His Sharingan would be even more powerful as he would know better how to use it. He might also be able to teach his younger self some new jutsu that he learned over the years.
Another theme is the exploration of relationships. Since Kakashi and Minato have a complex relationship in the original story, in time travel fanfictions, they can have new interactions. They might be able to understand each other better, like Minato getting to see Kakashi as a more mature and capable person if he travels to the future, or Kakashi seeing Minato's leadership in a new light if he goes back in time.
Maybe. If the fanfiction stays true to Kakashi's character in their eyes, they might approve. For example, if it shows his loyalty and skill, they could be okay with it.
Well, if Team Minato meets Team Kakashi in a fanfiction, it could lead to some epic battles or friendly competitions. Maybe they would have a sparring match to see which team is stronger. Team Minato with their speed and unique jutsus, and Team Kakashi with their diverse skills. Or they could collaborate on a mission, with Minato's leadership guiding both teams. It would be exciting to see how the different personalities interact, like Obito from Team Minato and Kakashi from Team Kakashi. They have a complex history that could be explored further in such a meeting.
Time travel can completely change their missions. They might have to redo a mission they already completed in a different way. For example, if they failed a mission in the original timeline, they could go back and try to succeed this time. Or they might have a new mission altogether because of the changes in the timeline that they caused through time travel.
Probably Naruto. Since Minato is his father, he has always longed to know more about him. Meeting Minato and his team would be a dream come true for Naruto. He would be eager to hear stories from his father's past, about his training, and how he became such a great ninja. Naruto might also want to show off his own skills to his father and the rest of Team Minato.
Well, it could be about Team Minato coming across Kakashi during a difficult mission. Maybe they find him in a tough spot and have to rescue him, and then they all work together to complete the mission that Kakashi was initially on alone.