Specifically on a Frigate.
Now my assumption is the component contains more than simple living quarters but is also essentially a nearly complete military base with training areas, stores, it's own armory and chow hall and whatnot. I'm thinking in the ballpark of about three thousand people as a medium sized occupancy that neither leaves it half empty nor overcrowds it, does that sound about right?
I tried looking in BK but the mustering and transporting sections don't actually say how many soldiers you can have, and obviously in a pinch you could cram way more into the ship by putting them in the cargo hold although then you wouldn't have room for cargo.