Ron could also be a key character. He might be a bit more hesitant about Harry's new state at first, but as a true friend, he would come around. He could be the one to make jokes about it to lighten the mood, like saying Harry should join the Gryffindor Quidditch team as a 'ghost - seeker' instead of a Seeker. But in serious situations, he would stand by Harry and even use his family's magic, like the Weasley's magic - enhancing items, to help Harry.
Hermione would likely still be a main character. She would probably be the one trying to research about Harry's half - ghost condition, scouring the library for any information on half - human, half - ghost beings in the wizarding world. She might also be the one to help Harry control his new abilities when they get out of hand, using her vast knowledge of magic.
Dumbledore could make an appearance. He might be the one who gives Harry the idea to become a pilot in the first place or provides some ancient magical knowledge about flying that helps Harry in his new career. Also, the Weasley twins could be involved. They could create some magical gadgets for the plane, like a device that makes the plane do cool stunts.
Dumbledore could still play a role, perhaps as a mentor from the shadows. Even though he's no longer alive in the original series, in fanfiction, his wisdom could be passed on through memories or portraits. He might offer cryptic advice to Harry about how to use his new power for the greater good and avoid the temptations that often come with lordship.
Hermione could be one of the main characters. She would be very helpful with all her knowledge of spells and magic theory. She could assist Harry in planning the layout of the village and ensuring that everything is in order.
Neville could play a role too. He has a deep connection to the magical creatures, and he might be sympathetic to Harry's idea of hatching the basilisk. He could offer some advice on how to handle the hatchling based on his own experiences with plants and other less - dangerous magical beings. Also, he could be the one to stand up for Harry when others start to question his motives.
Hermione could be one. She might come to the forest to check on Harry and end up staying to study the unique flora and fauna which have magical properties. Another could be Hagrid. He loves all kinds of creatures and the forest is full of them, so he could visit Harry often and bring him supplies.
Obviously, Harry Potter himself would be the central character. Then, Hermione Granger could be one of the members of the harem. She is intelligent and has a long - standing friendship with Harry. Ginny Weasley is also a likely candidate as she has a romantic interest in Harry in the original series. Luna Lovegood might be another, with her unique and dreamy personality adding an interesting dynamic to the harem.
Hermione could be one. She might help Harry take care of the pup, giving him advice on how to train it or what to feed it.
The Weasley twins could be part of it too. Suppose Harry yells in excitement or anger about a new prank idea that the twins have come up with that might be a bit too dangerous. They could either encourage his yelling or try to tone it down, depending on their mood. And Malfoy might overhear Harry's yell and use it as an opportunity to taunt him, adding more conflict to the fanfiction.
There could be Hermione and Ron. Since they are Harry's best friends in the original series, they would likely be important characters in this fanfiction too. They might be curious about Ducky and his relationship with Harry, and could even get involved in some of the adventures that are related to Ducky's past or his influence on Harry.
Hermione could be a main character. She might be initially skeptical about Harry singing muggle music, but then she gets interested in the cultural aspect of it and starts researching the history of the muggle music Harry likes.