In terms of campus, being in a city isn't the best plan because they need space. If you want to practice rescuing people from a sinking boat in a controlled environement or want to unleash a robot horde in an urban jungle, you need ot space to actually have those environments. A more isolated "colllege town" like place would work, the entirety of the area belongs to the school and it's sprawling enough to have a lot of variety. An island is great for that, because it can be big enough to encompass a lot of different natural terrains. Actually, the webcomic Magellan is about a superhero school that is a mobile island. Gives the security of being anywhere in the world with the all the benefits of beaches instead of miles of falling to your death.
One thing that might be interesting is looking into Supers, but alternative career paths. They touch on it in My Hero Academia, but not everyone can be a Hero. Super powered rescue workers, inventors, construction workers, ect, can be a way to spice up campus life.
Maybe the Hero class goes in an wrecks a city-scape in a practice bout of "villain fighting 101" and as they leave the construction/search and rescue classes are heading in to work on architecture and the repair work that comes with wrecking a few city blocks. And the relationships can go multiple ways, maybe one guy really likes the challenges the hero class leaves behind (how do I rebuild a building that was frozen as it was melting) while another is constantly annoyed at them because the house on LEgacy Avenue was their latest pet project and of course they had to level it... again.
As for clubs... what would football (american or otherwise) or rugby look like if superpowers were allowed? Getting involved in an inter-campus kerfuffle because of some crazy sport event could be cool, and it would allow for some interesting power uses. "Gerald loads the ball into his MK II launcher, blasting it off straight to the goal, but Linear intercepts, weaving back thru the opposing team with his shadow like body, can he take it all the- no, Concretia's wall has cut him off, she's diving for it" ect ect ect
Art clubs can get interesting with powers. Making things out of literal light, shaping materials in ways it was never meant to be shaped, actually, gives me a student idea too.
NPCs.
You need to have a janitor. He looks completely normal, no one knows what his power set is, but he is always everywhere, just quietly cleaning away at some brand new mess that was just created. I'd name him Jim, but I have no idea why. Maybe he has psychic powers, myabe he can make clones of himself, maybe he's just been at this job for far far too long and just has the knack, but it may drive your players crazy trying to figure it out.
For the art student, a girl who can enters people's dreams and tries to capture their "inner essense" in some of the most psychedelic, post-modern art you have ever seen.
For some reason, despite the fact you said freshman, I'm thinking there would be older kids around too, and I could see a senior whose got super toughness and constituton, which led him to a deep study of chemistry and ametuer brewing trying to make a drink that could actually get him drunk. Everyone knows him for his conconctions and forgets what his power actually his. I like supers who aren't defined by their powers, but by something else entirely.
Who are the outcasts in this school? Are they the ones who have powers that make them ugly and monstrous, or those who have powers that seem trivial and worthless. Either group could get a bit of mileage, and people who are self-concious because their powers make them look like monsters can always be interesting to work with.
Oh, from my game excerpt above, Linear is a guy whose a lot like Writhe, but his body mainly just turns into a shadowy line that looks like someone's taking a pen and drawing a line on whatever surface he's moving across. Concretia is a name I stole from Grrl Power, but the idea is a girl with stone powers. Stone form, melding, shaping, ect.
Student Council president is a guy with psychic powers, and everyone knows it, but he keeps getting elected every single time. A lot of times people will find themselves agreeing to do some odd job or other, only realizing later that he totally manipulated them into it. But he's a naturally charismatic and popular guy, and he never abuses his power in a way that gets him in trouble, just in ways that let him be a lazy busybody. I'm thinking of Breeze from Mistborn if you are familiar with it.
And the list could go on, but I should stop for now before I get too carried away.
