I was on a Florida State parent page for a bit before my daughter made her college decision. My impression was that housing was not a 100% guarantee even for freshmen (although there are many apartment options surrounding campus, so it’s almost like you’re on campus). It seemed to be a very competitive process, with a “housing deposit day” shortly after admission decisions are released, where students clamor to put down a deposit and get in a virtual line to pick dorms later in the spring. It forces a quick decision to either say “Yes” to FSU or put down the housing deposit anyway and risk losing a portion of it if your kid decides not to go (which many people do). Also, the pick list moves as those who put down deposits but weren’t sure about FSU, decide on other colleges.
I also noticed (and someone with a kid at FSU can correct me, if I’m wrong), that when picking a roommate, FSU recognizes the later of the two lottery pick numbers. So if one kid is #70 in the room pick and wants to room with some one who has pick #4,017 they both have to drop down to #4,017. I thought that was odd and that it must be hard for kids with bad lottery numbers to find roommates.
Upperclassmen/women can stay on campus (although I think the choices and spots are limited) - they have their own pick/lottery before the incoming freshmen pick.
My impression is that 4-yr on campus living guarantees are few and far between, and may be limited to much smaller schools than the ones you are looking at.