I really like the organic growth idea; moreso because my fortress always ends up very, uh, practical. I just do as I do, usually following economic approaches like "workshops - near 'finished goods' stockpile - near depot - near surface", but no fortess looks like the other. One time I decide to create one big "forge" area for all my metally needs, the other time I dig out "shopping streets" where every workshop has its own room and door.
As for the living area: I use 2x2 rooms for everyone; bed cabinet, chest. Usually its a 2 tile wide corridor with five 2x2 rooms on each side, but quite a lot of space beteen the rooms to upgrade them to 5x5 rooms or add another room or two. Thats easily done with two macros (one for designating the area, one for placing furniture).
Once my fortress progresses, certain dorf "earn" the right for a better room - Ill use the space for rooms and upgrades, like personal weapon racks/armor stands for great soldiers, a dining room for couples...
You could say I play Sim-Dwarf at that stage and I really like the diversity in the end

The basic rooms are done in 2 minutes, and the natural growth comes as time comes.