Hermione could be one. She might follow Harry to the island to help him out. Another could be Ron, his loyal friend. Or it could be some new characters created specifically for this fanfiction, like a wise old wizard who has been living on the island for centuries.
One main character could be a young witch or wizard who was born on the island and has a deep connection to its magic. This character could be Harry's guide at first, teaching him about the island's ways. Another could be a magical beast that Harry befriends and that becomes a sort of protector for him on the island. And of course, Hagrid could make an appearance. He might come to the island to check on Harry and bring some magical supplies from Hogwarts.
It could be Dobby the house - elf. Maybe he gets freed and decides to go with Harry to the island. There might also be a mermaid or a centaur character. The mermaid could help Harry navigate the waters around the island and the centaur could offer his knowledge of the island's magic. Also, Neville could be there. He could bring his unique skills with plants to the island, which could be useful for Harry.
Hermione would probably be involved. She could help Harry research about the island, like its history and any magical properties it might have.
There could be an old French wizard named Alphonse. He might be a mentor to Harry, passing on his knowledge of ancient French magic. Also, a young French witch named Celeste could be a main character. She and Harry could develop a friendship or more, and she could be part of Harry's new life in France, like helping him understand the French magical education system which is different from Hogwarts.
Hermione could be one. She might follow Harry to Australia to continue their adventures together. She could be interested in studying the different magical plants in Australia and how they can be used in potions.
Hermione would probably be one of the main characters. She's smart and resourceful, so she could help Harry with the administrative side of running the orphanage, like handling finances and paperwork. Ron might also be involved, perhaps teaching the orphans some practical magic skills. And of course, there could be some of the orphans themselves as main characters, like a young girl with a special magical ability that Harry discovers.
Hermione could be there. She would be really helpful in planning and organizing the island. For example, she might set up a system for categorizing all the magical knowledge and resources on the island.
Hermione and Ron would most likely be main characters. They are Harry's closest friends in the original story. Since Harry is deaged, they would play important roles in taking care of him or guiding him in some way.
Hermione would surely be one. She's smart and would be great at helping with the academic side of building a school, like creating the curriculum.
Well, Gandalf would probably be a main character too. He is a powerful wizard in Middle - earth and his knowledge and guidance would be crucial in a story where Harry is involved. He could be the one to help Harry understand the differences between his magic and the magic of Middle - earth. Also, Aragorn could be part of it. His leadership and warrior skills could be something that Harry looks up to or tries to learn from in this fanfic.
Ron might be there too. He could use his skills in handling magical creatures to populate the island with friendly ones. And he could also help with fishing in the surrounding waters using magic, providing food for those on the island.
Hermione could be one. She could come to Degrassi to help Harry. She'd be really good at handling the academic side of things there, like helping students with their studies. And also, she could use her magic knowledge to figure out any magical mysteries.