One possible plot could be that Harry uses his magical knowledge to create a bar with unique magical drinks. For example, he might serve Butterbeer with an extra kick of magic, or a potion - like cocktail that gives temporary magical abilities. He could also use the bar as a place for magical creatures and wizards to mingle, creating a new social hub in the wizarding world.
His old friends from Hogwarts would surely be regulars. Ron and Hermione would be there often. Neville might come to relax after a day of teaching Herbology at Hogwarts. Luna could drop by to share her latest theories about magical creatures while sipping on a strange - looking drink. Hagrid might also be a regular, though he'd need a special - sized chair.
It could be a magical creature - themed bar. Since Harry has a lot of experiences with magical creatures in the original story. For example, there could be pictures of hippogriffs on the walls and butterbeer with a special magical creature - shaped ice cube in it.
Hermione would be a great partner. Her intelligence and knowledge of magic would be invaluable. For example, if Harry opened a potion - making business, Hermione could handle the research and development of new potions, while Harry dealt with the business side like marketing and customer relations.
Her old Hogwarts friends would be very likely customers. They would come to support her new business and also to relive their old memories together. Hermione would probably come often to discuss books and new spells while having a drink.
Well, he might use magic to create the most amazing pastries. His Firebolt skills could translate to lightning - fast kneading of dough. And his Hogwarts friends would surely visit often, like Hermione might help with the bookkeeping using her intelligence and Ron would be there to taste - test everything.
Well, it could be a magic item store. He might sell things like rare wands, enchanted potions, and magical maps. After all, he has a lot of experience with these things from his adventures at Hogwarts.
Well, perhaps the plot could involve Harry using his fame and fortune to open an orphanage. He might use his magic to create a safe and magical environment for the orphans. Maybe he'd teach them magic himself, or bring in some of his Hogwarts friends as teachers. It could also show how he deals with the challenges of running an orphanage, like getting enough funds and handling difficult children.
Well, he might serve magical drinks like Butterbeer-flavored coffee. His cafe could be a place where wizards and muggles alike gather. He could use magic to decorate the place with floating candles and moving portraits. Maybe his friends from Hogwarts would help out, like Hermione managing the accounts with her intelligence and Ron being in charge of the food tasting.