>>52270853Goh/Koharu could be transfer students. It's pretty easy to move both of them from Kanto to Paldea thanks to the school setting. They wouldn't have to attend school all the time, either. Goh only shows up for school on rare occasions in Vermilion, so it could be the same in Paldea.
>>52270943Quaxly is my pick for Goh, too! I think they'd be cute together. Quaxly seems like the type that would act smug sometimes, and Goh has that personality trait too, so it would be fun seeing them mimic each other's behavior.
>>52270980Grookey will likely evolve before or at the very start of S/V and be left after Cerise Park, along with Inteleon. I can see Goh occasionally getting Professor Cerise to send him some of his Pokemon when he needs them/wants to see them, but the only one he'd probably keep on hand is Cinderace.