I figure that the cabins squeezed between other "working" parts of the ship falls in line with the idea of a packed ship of equipment with crew squeezed in. It reminds me alot of old navy ships that had bunk beds next to equipment.
I'm not sure "3" could be third-class as it does look very similar to other cabins. We don't get a good look into the second area though. Is it a work area like Rand's cabin? Or a second bed and he has a roommate?