I've decided to take a new approach, here is how it works:
16 dwarves in the fortress(initial group plus part of first migrant wave).
Lock system on the surface. Big room, trapped entrance and exit, lockable doors on both sides, big stockpile area in the middle.
When the migrant wave comes, open the external doors, lock the internal doors and wall them up. Migrant dwarves set to build/rebuild depot, harvest wood, do external construction projects---windmills, dams, waterwheels, channels, etc. Harvested wood and other useful items are stockpiled in central area.
When stockpile is full, reverse the locks. External doors locked, internal walls taken down, doors open. External stockpile removed and internal dwarves hall in the loot.
Rinse and repeat.
Keep a meeting place near the depot so you can keep track of inactive migrants and so that ambushes will come to the depot often. Keep depot up so that caravans including guards will arrive periodically. Caravan guards kill and are killed by goblins, kobolds, etc., which provides a steady supply of iron/steel armor/weapons.
Works great. I never risk my skilled workforce, nor do I have to feed/support more than 16 dwarves plus their children and a few cats. Migrants die frequently but are replaced regularly. Overall population stays low, yet value of fortress steadily increases.
Only real negative so far is that it prevents the training of a skilled trader.
