Kisame would probably be very angry at first. Samehada is his weapon and has been with him for a long time. He might feel betrayed and try to get Samehada back by force.
Naruto would likely win. Godlike Naruto implies he has extraordinary powers. Naruto has strong chakra reserves, and his signature jutsus like Rasengan are extremely powerful. Also, his ability to quickly adapt in battle gives him an edge over Orochimaru.
Iruka could be an important character. He's always been like a father figure to Naruto, and now with this new revelation, he might have to help Naruto deal with it. Hinata could also be in the story, and her feelings for Naruto could be complicated by his connection to Kisame. And then there could be some original characters created just for this fanfiction, like a ninja who was a former ally of Kisame and has some information for Naruto.
There could be. Fanfiction is a vast realm where all sorts of ideas are explored. However, I'm not sure if there is a highly popular or mainstream 'naruto is kisame apprentice' fanfiction. It might be a more niche concept, but it's entirely possible that some creative writer has delved into this idea to create an interesting story about Naruto learning from Kisame, perhaps incorporating Kisame's unique fighting style and view of the ninja world into Naruto's growth.
In some Orochimaru lemon fanfic, he might be portrayed as having a more seductive or alluring side. However, this is a very unorthodox view compared to his original character in the Naruto series. His intelligence and cunning nature might still be emphasized, but in a more sexually charged context which is not really in line with the official Naruto story.
He could have the power to instantly heal any injury. His chakra might be so vast that he can create multiple clones without getting tired. Also, he might be able to control the elements in ways that are beyond normal shinobi capabilities.
At first, it would be full of suspicion. Naruto is a Konoha ninja and Kisame is from the Akatsuki. But as the teaching progresses, they might develop a mutual respect. Naruto would respect Kisame's power and knowledge, and Kisame might respect Naruto's determination.
One idea could be a story where Naruto and Kisame are forced to team up during a mission that has a greater threat to the ninja world. They start off distrusting each other but gradually come to respect one another's skills.
Well, in some fanfictions, Naruto might defeat Kisame in a battle and take the sword as a trophy. Maybe he uses his newfound Sage Mode powers or some other advanced jutsu to overpower Kisame and claim the sword.
In a fanfic of Kisame and Itachi taking Naruto, it might explore the relationship between the two Akatsuki members and Naruto. Itachi has his own complex reasons for his actions, and Kisame is his loyal partner. When they take Naruto, Itachi might be conflicted as he has a connection to Naruto through Sasuke. They could end up in a situation where they have to make a choice about what to do with Naruto.