Hermione would be a great help. Her vast knowledge of magic and books could provide the necessary information for building the planet, like the right spells and magical theories.
Dumbledore's spirit or some form of guidance from him might assist Harry. Dumbledore was always full of wisdom, and his knowledge of magic was profound. He could offer insights on creating a balanced and sustainable magical planet, ensuring that the magic doesn't go out of control.
Ron could also be there. He might not be as book - smart as Hermione, but his loyalty and courage would be useful. He could help Harry with the more physical aspects of building, like moving large magical objects around the planet - in - the - making.
Well, perhaps Harry uses his magic to shape the planet. He might create unique magical creatures and ecosystems. For example, he could make a forest where the trees are made of living fire that doesn't burn but gives warmth and light.
Dumbledore might help in a spiritual or advisory way. Even though he's passed away, his wisdom could be passed on through memories or some magical means. Also, Hagrid could be a great help. He could assist in building areas suitable for magical creatures with his love and understanding of them.
His friends Hermione and Ron would most likely be his allies. They have been with him through thick and thin in the original series.
Maybe an old wizard who has been secretly studying the combination of different magical universes for years. This wizard could have made some initial attempts at building a lightsaber - like weapon in the past and can share his experiences and mistakes with Harry. He would teach Harry about the balance between the light and dark side of this new form of magic, just like the Jedi teachings in Star Wars.
Ron could also be a great ally. His loyalty and courage would be important. He might be in charge of security, using his skills in wizard chess to plan out defensive strategies. And of course, the Weasley family in general could offer a lot of support, with their various skills and connections in the wizarding world.
The Ministry of Magic would probably oppose it. They are always concerned about maintaining the secrecy of the wizarding world and a stargate could potentially expose it to non - magical beings or lead to unwanted magical interference from other realms.
Hermione could be a main character. She would use her intelligence and vast knowledge of magic to help Harry plan and build the city. Her skills in research and spell - casting would be invaluable.
His character could develop in terms of leadership. As he is building the ship, he has to take charge and make decisions. This would make him more confident in his leadership abilities.
His best friends, Hermione and Ron, would surely help. Hermione could contribute with her intelligent ideas and knowledge of magic for construction. Ron would be there for the physical labor part, using his strength.
In a fanfiction, Harry Potter could be in a situation where he needs to recruit players with strong muscles for the Quidditch team. He might search through Hogwarts to find students who have been secretly training and have the physical strength required for the tough positions in the game, like the Beaters.