In short, it's not my job to come up with an antagonist for this story, it's above my paygrade, let the DPC do his job. "Here we are now, entertain us"
Being serious, I can't point to a specific person and say "that's the antagonist". Vinnie looks like a proper villain material, he is chaotic and dangerous, and can easily become the spark that burns to the ground the fragile world of B&R. But I don't think he's too important to be the main antagonist, he's more of a chain of events fuse. Something like Vinnie hitting hard or shooting at the MC. Or he aims at the MC, but shoots someone near him, someone who is dear to the MC, Jill for example. Hello drama, my old friend!
Anyway, after the incident, the cops intervened, the investigation begin, the Quinn's buisness is exposed, the connection with Burke is revealed, a huge scandal, everything is ruined in B&R. Headlines: "B&R University was front for drug dealing and prostitution.", "Dean Burke denies any involvement in buying sexual services from students. Several students had previously accused him of harassment.", "New evidence of drug-dealing activity on campus grounds has been unearthed, including on a fraternity house run by the son of one of B&R's co-founders." (same goes for the sorority house, run by the daughter of dean Burke). I'm sorry here for my English, I feel that I may sound ridiculous but I can't correct it myself.
I think there is more than enough fuel for the drama. The Sage's arc alone is worth something! Her father is a predator in disguise, her sorority is a whorehouse and drug store, her university has gained a reputation, her mom cheats on Sage's dad with Sage's boyfriend. Hey Fuckface, antagonize this
Another direction an antagonist might come from is the MC mom's lineage. I find it hard to believe these conspiracies about Jill's blood relation to the MC through his mom. But we know almost nothing about his relatives from his mother’s side, only that they have been assholes to Neil and the MC all their lives. Maybe one of them is going to interfere and ruin the MC's life.