Cadets, DamCon team members, Marines (possibly part of the security you mentioned). Not sure if I can think of anyone else off the top.
Larger quarters for the lower ranks/enlisted might not be a bad idea considering space conservation. We could even go with some rooms with several sets of bunks, almost like a barracks, if we really wanted to. If we can narrow a lot of this down maybe one of us could start working on some floor plans.
As for crew sizes, based on the numbers suggested, I’d say the Battlecruiser would be comparable to a Light Cruiser, maybe 10 or so more based on the slightly larger hull. And I’m guessing a Missile Cruiser and Battleship both might house around 100-120 or so.