It's possible that Harry could encounter some old enemies in disguise. In the world of Harry Potter, there are always dark wizards or witches trying to infiltrate the Ministry. They might be there during the Owls event, and Harry would have to be on his guard. He could also meet some new allies, perhaps some young witches or wizards who are also taking their Owls and end up joining forces with Harry in some way.
He might meet Hermione. Since Hermione is always interested in academic things like Owls, she could be there to help Harry or just be involved in some research related to it.
Well, in this fanfic, perhaps Harry could face some unexpected challenges during the Owls at the Ministry. Maybe he discovers some new secrets about the Ministry's operations related to the Owls.
In the fanfic, Harry Potter could meet the new generation of students. They would be in awe of him. He might also encounter some of the ghosts, like Nearly Headless Nick, who would surely have some interesting stories to share since Harry left. And there's a good chance he'll meet the caretaker, who would probably give him a hard time about coming back and causing a stir. Moreover, he could cross paths with some of the older students who idolize him and want to learn from his experiences.
His friends from Hogwarts like Hermione and Ron would most likely support him. They have always been by his side through thick and thin in the original story, so in the fanfiction, they would continue to support Harry in his fight against the Ministry.
The Order of the Phoenix members might also back Harry. They've fought against the dark forces before and if they see that the Ministry has become a threat, they'd side with Harry. Dumbledore's old allies in the Order would believe in Harry's judgment and join him in his mission to destroy the corrupt Ministry.
Hermione would definitely be one of his top allies. With her intelligence and knowledge of the wizarding laws, she could help Harry in making important decisions regarding Ministry policies. Ron would also be there, providing his loyalty and courage in times of trouble.
Harry might encounter some magical nomads. These are wizards and witches who don't settle in one place but travel around the wizarding world. They could introduce Harry to different cultures within the wizarding community and show him some unique magic that he has never seen before.
His friends like Ron and Hermione would surely support him. They have been through a lot together, and they believe in Harry's leadership. Also, the Weasley family in general would be behind him. They have always been on Harry's side in his battles against the dark forces.
He might meet the house - elves that have been taking care of Potter Manor for generations. They could show him around the manor and tell him stories about his family.
He might meet some old retired wizards who can tell him stories about the old days of magic. For example, they could share tales of how Hogwarts was founded or the great wizarding wars long ago.
He could meet other young wizards and witches who are also working summer jobs. Maybe some from other wizarding schools.