I'm not too sure. I've had numerous pairs from 377-391, and none of them married even though they've all idled for the past half a decade or so. If I have to let 40 migrants in just to get a breeding pair, it kind of beats the purpose of the whole project. Not to mention you need at least 2 breeding couples at the same time to produce offspring within the 10 year age requirements.
I think I'm going to consider my attempt a failure at this point. 18 dwarves total, 2 killed.
Farthest building to the left was the new tavern/social area. Directly right of it was the industry district, with various workshops and a small office tower.
North is the covered bridge, and housing for the migrants.
Farthest right is the hospital, which became necessary after Bear's attacks. Bear is a dwarf.
Farthest south is the jailhouse, with 2 cells. Bear spent almost 3 years there after brutally slaying 2 dwarves, injuring atleast 3 others, and fracturing the sheriffs spine. Clearly, someone should have made him a pair of pants.
Very bottom of the image shoes the tombstones of Bear's victims. My favorite part about this experiment was burying dwarves the old fashioned way, then memorializing them.
For future attempts, I would suggest a few things.
1: Mod the marriage rates to be nearly 100%, as mentioned in the other thread. As long as dwarves match in terms of sexuality, they should marry. Many of my couples were "Dreams of starting a family" type dwarves, and still do not marry.
2: Mod out all fliers. a single eagle is enough to drop my FPS from 250 capped to about 160. A gaggle of ravens is enough to drop me from 250 capped to about 90. I ended up using dfhack to kill fliers to keep them from bombing my FPS every 2 minutes.
3: Mod out "critter" type animals, like fluffy wamblers, rats, etc. Every season 2-3 would escape from the traders and become part of my fort. They can't be killed or adopted or anything, and clutter the heck out of the animals screen. I'm not sure if they contribute to the animal cap or not, but my dogs and sheep stopped breeding after a while, despite having rather low numbers.
I don't think it's possible to get a sustainable population from 4 or even 7 dwarves. It has to be a perfect storm of random variables to get at least 4 dwarves who are straight, interested in marriage, opposite sexes, and within 10 years apart. And then you need to repeat the process with their children, with the added problem of having to wait 13 years for them to mature into adults to find out.