As time has gone on (I have been playing for about a year), my hallways have gotten larger and my living quarters have gotten smaller.
I started with 5x5 bedrooms. I eventually turned off economics so that I did not have a bunch of bag-Dwarves sleeping in the hallways. With a grand dining hall, plenty of superb booze, and food ranging from raw rat weed up to masterpiece roasts, my non-nobles are content with a 2x2 room and a bed. Married couples get an additional bed for the spouse, even if they don't really need one. I just wish that I could still assign rooms after the economics kicks in. I would like to resettle families into their own sections as they have more children. But, oh well.
I started with 1-square tunnels, and wondered why everyone did that funny blinking while they walked. You know, the one that means Dwarves are lying down on the floor so others can pass?
Then I got really expansive and gave them 2-square tunnels. Eventually I got up to 6 for the mains and 3 for the alleyways. In my current fortress I am experimenting with a design that is 6-squares and 8-squares for the main hallways, alternating, and no alleyways. I think I am getting less overhead from pathing. With the new design I am also making all walls 2-squares thick so I can be sure the engravings are on the side where I want them to take effect. It will cut down on the number of rooms that I can put on one level, but hey, I hardly ever use more than three levels anyway. Five levels of rooms will not be a big burden, and it will make me feel more as if I am getting some use of the rest of the area.
Like others, I tend to place my farms in the top couple of layers. That is because that is where the dirt is located. Milling needs to be one layer underground if wind- or watermills are used. That means that the raw food needs to be stored in those top couple of layers, and the rest of the food follows as well as the textile industry. Butchering, and therefore tanning and leatherworking, also follow.
The dining room needs to be down far enough to be located in rock so that it can be smoothed and engraved. The homes for the nobility have the same requirement. Since bedrooms for all the Dwarves need a quiet area, those tend to end up in the nobles' neighborhood also.
Woodworking, stonecarving, glassbowing, gemcutting, masons, mechanics, and bonecrafting can be where-ever it is convenient, but preferably on the opposite side of the dining hall from the bedrooms. Stockpiles in dirt levels are more convenient, but this is balanced against the nuisance of digging under surface water (What, damp stone
again? Try the next square ...) and the danger of too much sprawl. My current fortress is the first one in a long time that has no magma, and I am enjoying the freedom from having to drag everything off to one corner of the map to accommodate the magic eternal fuel supply. Of course, without coal seams I would be in very bad shape without the magma, but it is still a welcome relief.
One lesson I learned again today is: Keep the traps outdoors!!! You cannot use the "go outdoors" settings to control the Dwarves from cleaning the traps if you put the traps inside. I lost a pile of good workers who just could not quite believe that there were goblins
right there in the hallway, yes indeedy. However, having the trade depot indoors is a good thing. It means I can carry out trade while the goblins are impaling themselves on Large Iron Daggers outside the entrance.