I'd like to post here two of my methods of fortress-building, both of which have been tested, and which are intrinsically linked.
The main concept is of Dwarven Contractors (AKA Slave Gang).
The idea here is that the dwarves embark with 6 miners/engravers + 1 mason/mechanic (optional) and just enough food to last a year. They work till out of food, then are executed. You then come back to reclaim and repeat; until you're happy and ready to move in permanently.
The second and more important method is the Adamantine Strip Mine.
Essentially just 7 miners who embark a 2x2 area with HFS. They mine it out, being careful not to dig too greedily and too deep, (at least until the very end) and then extract strands 'til the food runs out. You come back in adventurer mode, then transport all the strands/raws you can carry to a previously established site (either a pre-gen'd one, or an old fortress of yours). If you reclaim an old fort with all that brightbluegold in it, you should (haven't tested this part yet) get at least 100+ dwarves on embark, depending on how many strip mines you made.
This method may be very useful for setting up a community fort in, say, the Age of Death; as the high number of starting dwarves will make for some interesting social interactions.
(P.S. Speaking of the age of death, do animalmen count towards that? With the new camps for them, unending combat may have become possible against the savage, degenerate mutants that survived the Thermonuclearkitty War.)