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.
I think the house - elves would be involved. They are very good at building and maintaining things. They could use their magic to quickly construct buildings and keep the town clean. Also, Neville could be a big help. He has become quite powerful and his skills in herbology could be used to create beautiful gardens and magical plants around the town to make it more lively and functional.
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.
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.
His friends Hermione and Ron would most likely be his allies. They have been with him through thick and thin in the original series.
Some of the Hogwarts professors could also assist. Professor Flitwick could use his charms expertise to add special touches to the city - ship, like making the doors open with a unique charm. Professor McGonagall could use her transfiguration skills to transform materials into the needed shapes for the construction. And Neville could also play a role. He has grown into a powerful wizard, and his knowledge of herbology could be used to create a beautiful and functional garden on the city - ship.
Dumbledore (if he were still alive) could be an advisor. His wisdom and experience would be invaluable. Also, some of the Weasley family members like George, who already has experience in running a joke shop, could bring his business acumen to Harry's company, helping with sales, marketing, and product design.
Neville could be another helper. He has become quite skilled in herbology. He could help Harry by creating a magical garden around the house. The plants in the garden could be used for protection, like thorny bushes that keep unwanted visitors away, or for providing ingredients for household potions.
Dumbledore might help from beyond the grave, in a sense. Harry could discover some of Dumbledore's old notes or memories that provide crucial insights into building a powerful and controlled bomb. And perhaps some of the more eccentric professors at Hogwarts, like Professor Flitwick, could offer their expertise in charms which might be needed for the bomb's construction.
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.
His friends from Hogwarts, like Ron and Hermione, are likely to help. Ron could bring his family's practical knowledge of wizarding homes and Hermione would contribute with her extensive research skills.
The plot could involve Harry Potter building a town that is a blend of the Muggle and magical worlds. He could build schools that teach both magic and Muggle subjects, houses that have both magical and non - magical features. He wants to create a place where wizards and Muggles can co - exist and learn from each other. This would be a revolutionary idea in the Harry Potter universe and would attract all kinds of people, leading to many adventures and challenges along the way.