I always use caste systems on e way or another. Over the years and countless forts I used 4 castes, changing names from time to time:
nobles - monarch, duke, any consorts;
professionals (sometimes "patricians") - dwarves dedicated to a certain skill, usually 15-20% of population;
soldiers (or "defenders") - every non-specialized male dwarf, trained to high master in pump operator to give them civilian profession;
workers (farmers, plebs, peasants, etc) - all non-specialized female dwarves, doing farming, wood burning and furnace operating;
sometimes also a "police caste" of 1 or 2 squads worth of marksdwarves for simplicity.
As for living, my current for can be an example (I can't export it to map archive properly for some reason, I just exports ASCII without graphic set (obsidian), anyone knows why?).
It's an above-ground fortress, with central large tower: 1st floor - trading depot, statue garden in future; 2nd - legendary dormitory, dining area, stockpiles of booze and prepared food; 3rd - workshops and 4th - offices/jail/hospital.
And than there are 4 smaller towers around it :
southern is for soldiers with barracks, training areas, also the only entrance to fortress is through this tower;
western is for workers, with 11 3x3 rooms per floor, for 44 workers (I have 42)
eastern is not built yet, but will have rooms for 20 professional workers
northern is unbuilt too, it was supposed to be queens and nobles personal tower, but I decided to build queen's tower using gold on top of the main one isntead, so this tower will be a masoleum/cryps.
So all castes are somewhat spread out, using the main tower as central hub for work and food/drink.