Another character could be a cologne - making elf. In the wizarding world, there could be elves who specialize in making colognes. This elf could have a special bond with Harry. It could be that the elf was tasked with making a special cologne for Harry's protection from the moment he was born. And as Harry grows, the elf helps him understand the true power of the colognes he has been surrounded with all his life.
Well, it could be that Harry is raised in a world where cologne has some sort of magical property. Maybe the scent of a particular cologne is used to protect him or give him special powers. For example, the cologne might be made from rare magical ingredients and whenever Harry wears it, he can blend into the Muggle world more easily because it masks his wizardly aura.
Dumbledore could make an appearance, even if it's in a memory or as a guiding spirit. His wisdom would be invaluable in setting up the guard. McGonagall too could be involved, she could help with training the new guard members in discipline and magical skills. Then there are the Weasley twins. Their creativity with magic could be used to create some unique security measures. They might come up with enchanted objects that can detect and repel any intruders. And Hagrid could also be part of it, his strength and his love for all creatures could be an asset, perhaps he could use some of his magical creatures to keep an eye out for danger.
Hermione could be one. She might follow Harry to America to continue their adventures together. She could help Harry adjust to the new place with her intelligence and knowledge.
There could be the mob boss who takes Harry under his wing. This boss would be a key figure, teaching Harry the ropes and acting as a sort of father figure. Maybe there's also a rival mob member who becomes an antagonist in Harry's story.
Ron could also be in it. He might initially not believe that Harry is hiding his intelligence, but as the story progresses, he could start to notice little things that Harry does which show his real intelligence. Ron's loyalty to Harry would then play a role in how he reacts to this discovery, either helping Harry keep it a secret or getting frustrated with Harry for not sharing his intelligence more freely.
Hermione would probably be one of the main characters. As Harry's friend, she could be a teacher at Hogwarts, perhaps the new Transfiguration teacher. She would offer her intelligence and knowledge to support Harry in running the school.
Ron and Hermione would surely be there. Ron might be a bit hesitant at first about Harry raising a dragon, but he would come around to help. Hermione would use her vast knowledge of magic and creatures to assist Harry in taking care of the dragon.
Ron could also be important. He might be torn between his loyalty to Hogwarts and his friendship with Harry. Eventually, he could choose to leave Hogwarts to be with Harry, bringing his Weasley family charm and his own brand of magic to the group. The Weasley twins might also get involved, providing some much - needed humor and their unique magical inventions.
Obviously, the muggle actress, his late wife. Her friends from the acting world could also be important characters. They might come to check on Harry and the kids, if they had any, and share stories about her time in the acting business.
One possible main character other than Harry could be a local journalist named Ben. Ben might be intrigued by Harry's story and decide to write an article about him. Also, there could be a Canadian mountie, Officer Davis, who initially is suspicious of Harry but later becomes his ally as he learns more about Harry's situation.