There could be some old family friends or allies of the Potter family that surface to offer assistance. These could be other pure - blood families or even some members of the Order of the Phoenix who have a connection to the Potter family's history and want to see the manor restored to its former glory.
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.
Well, in fanfiction, Neville Longbottom could be one of the visitors. He and Harry could exchange gardening tips as they explore the manor's gardens. Additionally, Dumbledore's portrait might be magically transported to Potter Manor, and he could offer his wisdom and guidance to Harry as he lives in the manor. And of course, Hagrid might come with some magical creatures to show Harry, adding more excitement to the manor.
Perhaps during the rebuilding, Harry has to deal with various magical creatures that have made the ruins of Potter Manor their home. He might have to find a way to relocate them without harming them. Also, he could be visited by friends from Hogwarts who offer their help and in the process, there are some interesting interactions and exchanges of magic knowledge.
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 might also play a role. He has vast knowledge and experience. He could offer some wise advice or even provide a special magical item or spell that is crucial for the unicorn's healing.
Dumbledore might offer some guidance. He has vast knowledge and experience. He could tell Harry about the significance of different elements in a staff and how to combine them to make a truly powerful and unique magical tool.
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 best friends Hermione and Ron would surely be there to help. Hermione with her vast knowledge of magic could research about the egg, and Ron with his loyalty would stand by Harry's side in any danger related to the egg.
It's possible that an old acquaintance from Hogwarts who has family ties in America could assist him. This person might already have a network in America and could introduce Harry to important people. Also, there could be some reclusive magical scholars in America who, out of curiosity about Harry's powers and his role in the UK, decide to help him. They could teach him new magical skills that are specific to the American wizarding world.
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.
Hagrid would be a likely helper. He has a great knowledge of magical creatures and would surely know a lot about phoenix eggs. He could give Harry advice on how to take care of it.