Definitely Hogwarts students. They'd come during their free time or on trips to Hogsmeade. They'd be eager to try Harry's special magical treats.
The employees of the Ministry of Magic would also be regulars. They'd stop by on their lunch breaks or after work to pick up something sweet. It could be a place for them to unwind and chat with other wizards.
His Hogwarts friends would probably be the first. Hermione would be eager to check out any new books or intelligent - enhancing potions. Ron would be interested in any food - related magical items, like everlasting candies.
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.
I think magical creatures would also be customers. Maybe house - elves would be sent to pick up treats for their wizarding families. Hippogriffs might be lured by some special bird - shaped pastries. And even centaurs, if they were feeling a bit more adventurous, could come to the edge of the Forbidden Forest where the bakery might be located to get some goodies.
Other potion shop owners might visit too. Not as customers in the traditional sense, but more to check out the competition. They might be curious about Harry's unique potions. And then there are the local wizards and witches in the area where the shop is located. They could need potions for daily life, like a potion to make their gardens grow better or a potion to keep their pets healthy.
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, perhaps Harry uses magic to create the most amazing and unique pastries. He could make cakes that levitate a bit when you cut into them. And his potions knowledge might come in handy for creating special flavor combinations that Muggles have never tasted before.
Hermione would probably be one of the main characters. She's smart and resourceful, so she could help Harry with the administrative side of running the orphanage, like handling finances and paperwork. Ron might also be involved, perhaps teaching the orphans some practical magic skills. And of course, there could be some of the orphans themselves as main characters, like a young girl with a special magical ability that Harry discovers.
It could be Hagrid. He loves all kinds of magical creatures and would be very interested in seeing what Harry has in his pet shop. He might even give Harry some advice on taking care of the more dangerous ones.
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.
Hermione would probably be a regular. She'd come to the cafe to study while enjoying a warm cup of Butterbeer latte. She might even bring some books from the Hogwarts library to read there.