I think that once Burrows are in, you'll see more varied housing designs. Right now, because it's difficult to make dwarves work rationally, efficiency is key. If all of your hauling jobs are within 100 steps of each other, it doesn't matter that your dwarves will take hauling jobs that are the farthest from where they currently are, despite there being a hauling job in the tile that they're currently standing in.
Fort design reflects this. The fractal designs, while the they look neat, are also designed to make walk distances uniform. If the dwarves generally walk the same distances to perform their vital functions, and generally walk the same distances to perform their fortress functions, then they generally take about the same amount of time to do anything - so you can more easily strike the right balance of crafters and haulers. You won't have times when your 50 haulers are doing nothing because all the jobs were right next to each other (and then you have to break up a party), and you won't have times when you're hauling list is backed up to over 500 tasks because all your haulers decided to haul ore from one corner of your map to the other.
Now, when burrows are implemented, you can assign haulers who's jobs are to specifically keep the craftsdwarves shops clear, and assign haulers who's jobs are to specifically pull ore out of the ground. I bet you'll start seeing more variety. The mines across the map will have a miner and a handful of haulers living there - maybe smelters, woodcutters, and woodburners, too. They'll transform that bulky ore into nice, compact bars, which more dedicated haulers will drag into your fort proper so it can be turned into gaudy, gem-studded buckets or something. These smaller sub-forts will probably be rebuilt somewhat frequently as mines play out.
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I just realized I ran off on my own tangent, and didn't actually answer your questions...
How do you make dwarven housing scale to accommodate 200?
That really depends on if you have the economy turned on or not. If it's on, probably with many large barracks. If it's off, Multiple layers to reduce walk time. The 3x1 room isn't glamorous, but it's enough to make dwarves happy (ecstatic, even). Ideally, the longest travel hallway won't be much longer than the tallest staircases. A 10x10x10 block holds 1000 tiles, and has a longest walk distance of 30, if your design sucks. A 30x30 block hold 900 tiles, and has a longest walk distance of 60, if your design sucks. Stacking is where it's at. Make something that will accommodate, say, 20 dwarves, and stack it 10 times. There you go, 200 dwarf accommodations. Blocky apartments are easy to designate (heck, just make a grid, and use un-designate to chop it into separate rooms, and then re-designate the hallways. You can make a surprising number of rooms with very little effort or thought this way)
How are children dealt with?
For a little while at least, they live with their parents. I just make tons of rooms and leave the beds designated as bedrooms, but not assigned. Dwarves needing a bedroom (or, for some nobles, 3 or 4) will just grab one. Honestly, I have no idea when children move out, I let the dwarves handle that. It does make it somewhat annoying to try to find a depressed dwarfs bedroom to try to spruce it up, though.
How many dining rooms/offices should dwarves share?
The reason why you see a lot of massive dining halls with seating for everyone is because that's really the easiest way to ensure everyone's always eating in legendary dining halls - even if it's filled with granite tables and chairs made by a dabbling mason, enough of them add up to legendary. Depending on fort design, you may decided to make other dining halls (say, for your magma operation, so they don't walk across half the map for a snack). Just make sure there's enough stuff in there to make it legendary (not difficult for a mature fort with skilled craftsmen and lots of materials to decorate with - just put in a masterpiece aluminum throne studded with every metal and gem you have, and it'll probably end up making the place legendary by itself).
Same for offices really, except that very few dwarves need an office. Just some of the nobles and the bookkeeper (who's happy with his 'barely above squatting in the mud' quality office). Making a massive super-office is just another lazy/efficient thing. With enough bling, even a 5x overlapped office will still be royal for everyone. Especially if you make it in a gold seam or something - those engraved floors add up, fast.
For aesthetics, I always make my bedrooms 3x3, and they have a bed, a cabinet, a chest, a table, and a chair. If I notice married dwarves living together (since I rarely even look, this doesn't happen much), I'll add another cabinet and table/chair combo. I sometimes see dwarves eating in their room, but it does happen.
Personalized food stockpiles?
Too much effort for me. The main problem is getting the food onto the stockpile in the first place. Stockpiles can only have one stockpile taking from it, and your main food stockpile is going to get all the food - because if it's not the closest thing to your food source, you're wasting a whole lot of hauling time. Add these two things together, and you realize it's very, very difficult to ensure everyone's personalized food stockpiles are actually stocked.
Keep in mind that it is possible, if you make individual 'base' stockpiles for each kind of food near your production, then use long, long chains of 'take from' you can eventually get everyone's personalized food stockpiles (in actuality, 4 or 5 one or two tile stockpiles that can only hold one type of food/drink) more or less stocked constantly, but at the cost of an absurd number of hauling jobs.
Burrows may help with this, since you could (with great effort) sort your dwarves by preferred foods and just direct all of that kind of food to that burrow).
Overall floorpplan?
This one is tricky - and highly individual. For me, since it often varies based on what resources are around. Industry tends to center around magma (if available), and food production tends to center around soil (so I don't have to mess with irrigation). Depending on map layout, housing is either to the side, or between those two major economic zones. I generally tend to go with the "major hallway" approach - a 4 or 5 tile wide hallway that spans the length and breadth of my fort. For some reason I prefer ramps to stairs, which makes my overall designs somewhat corkscrew-like. As I stated earlier, building in layers are great. My industry is usually a massive storeroom with non-fueled workshops above, and fueled workshops below. I use two 3x4 workshop rooms linked by a short hallway with doors for each workshop and an up/down stair between the doors. The extra space between the doors and the workshop proper is for cage traps, to be build if a moody dwarf claims the workshop - insanity is safely contained before they can hurt anyone else. The extra space in the shop itself is for small and specialized stockpiles for whatever materials the dwarf uses. Not so useful for craftsdwarfs (they go through a ton or rock/bone), but great for jewelers, because even a 3x1 stockpile can hold a ton of gems.
Basically:
+----+ +----+
|....+---+....|
|.....DXD.....|
|....+---+....|
+----+ +----+
I like this design because it's very, very stackable and repeatable.