One interaction could be that Sakura is initially a bit intimidated by Kakashi's reputation, but as they work together more often, she becomes more comfortable around him. Pakkun, on the other hand, might be very protective of Sakura. He could growl at Kakashi if he feels that Kakashi is being too hard on her during training. And Kakashi might just chuckle at Pakkun's protectiveness and respect his loyalty towards Sakura.
One possible plot could be an adventure where Kakashi, Sakura and Pakkun are sent on a mission together. Pakkun could use his tracking skills to lead them to the target. Sakura, with her medical and combat skills, would be there to support and fight when needed. And Kakashi, being the experienced ninja, would strategize and protect the team. Maybe they have to retrieve a special artifact that is hidden deep in a forest filled with various traps and enemies.
I'm not sure exactly who the best authors are as it can be subjective. However, you can look for authors who have a high number of positive reviews on fanfiction websites. They usually write engaging stories that stay true to the characters of Naruto and Pakkun.
One interesting 'Naruto Pakkun' fanfiction could be about Pakkun's adventures before he joined Naruto. Maybe he had some secret missions in other villages. Another could be a story where Pakkun helps Naruto in a different way during a difficult battle, like using his unique tracking skills to find a hidden enemy base.
Often, Gai is paired with Kakashi in Hurt Kakashi fanfiction. Gai, with his unwavering belief in friendship and his eternal rivalry with Kakashi, can be a great character to interact with a hurt Kakashi. He might try to pull Kakashi out of his slump through their friendly competition. Also, Rin is sometimes included. Since she has a significant past with Kakashi, her presence in the fanfiction can either be a source of comfort or more pain, depending on how the story is written.
In such fanfiction, the Kakashi OC often has unique physical features. For example, they might have distinct hair color or eye shape that sets them apart.
Kakashi might be initially surprised. But then, he would probably use it as a teaching moment for Naruto. He could say something like 'Naruto, stealing is not the way of a ninja.' And then give him a punishment like extra training.
Often, Naruto is paired with Kakashi in such fanfictions. Their bond from the original series can be explored in new ways in the context of Kakashi's reincarnation. For example, Naruto might be the one to discover Kakashi's reincarnated form and help him adjust.
Kakashi could use his Sharingan to analyze Obito's moves and find a weakness in his defenses. Since he has the Sharingan, he might be able to predict Obito's attacks and counter them effectively, eventually finding an opportunity to break free.
Kakashi's reaction would be complex. He is a man who has lost many people in his life. But Naruto was special. He would hold Naruto tightly, his hands trembling slightly. He might try to use some of his own chakra to keep Naruto alive a little longer, but deep down he knows it's futile. His face would show a mixture of pain, regret, and love. He would remember all the times he trained Naruto, all the lessons he taught him, and how Naruto had surpassed all expectations.