Let's see... Maizie has an incredible sweet tooth and I think their personalities would mesh pretty well, since Maizie can be pretty bright and bubbly herself at times.
Dani would be a little more reserved in the face of Shelby's excessive optimism, but if the Doughnut Hole has tables, I could see her studying there sometimes. Or maybe she and Shelby will have a class in common and could interact at the school. (She's taking primarily science, so maybe they'd overlap in a bio course or something?)
Bunny definitely shares the sunshine and optimism trait, so I think she and Shelby could hit it off. And Bunny can appreciate some well-made baked goods.
Kevin will probably wander in at some point too, and I can't think of any reason why they wouldn't get along. He's outgoing and generally pretty good at befriending people, so they could probably hit it off just by virtue of the fact that they're both extraverts. Her sassy personality would probably find a pretty good reception with him.
Amanda might think that Shelby's optimism is a little misguided, but she appreciates anyone who's willing to come into the city and start a business. So that gets Shelby (and her Gram!) into Amanda's good books.
We already touched on Pikachu in his intro but yeah, safe to say that he and his daughter will be regulars!