You should be ok for the first couple gens.
Founding Seven
- Take an extra pick & training axe. forbid and leave them for the migrants to use.
- Dig down a couple z-levels. build a farm.
- Dig down to magma while carving resupply minecart tracks. finish housing at the farm
- Set up magma forges and get to work
- Once kitted out, you can spend a few years training or immediately seize and wall off part of cavern 3 for a easymodo farm and trees.
- Plan out watersource breach, plumbing, main reservoirs, wells, redundant reservoirs & wells, water reactor bank, irrigation tanks, Power conduit, redundant backup conduit in-case of disassembly, sealed storeroom holding mechanisms and blocks to make quick repairs.
- Dig out previous except for the breach. add in shutoff bridges in case something somehow gets in.
- If you haven't already, weapon trap the shit out of the deepfort with multiple panic rooms. Safety of the 7 comes above all. Stock picks & a bag of wheat seeds in all of them.
- breach the cavern. all 7 need to quickly build the intake platform and get floor grates over the intake asap.
- fill wells, reservoirs, irrigate via flood/bucket. Get a tree farm up.
- Find and smelt reagents for black bronze
- Black bronze errything all day errydday
- Once all furniture is black bronze start plating the floors
- Profit
Migrants Build a surface fort surviving on masterwork whip vine flour roasts and shooting gobbos with wood bolts and metal bolts ordered from the humans and dwarves with 20,000 dwarfbuck roasts. Your Deep Dwarves will most certainly be Jelly.
Deep dwarves get to slab makin in case the surface gets rolled for whatever godawful reason. Build a grand mausoleum plated in black bronze.
It'll be like any other fort except you have a bunch of mad-dwarves on the magma sea.
!!Doubleplus Omake!! Build a buildingdestroyer baited false entrance to trap and train trainable cav:3 beasts. Perhaps have them fight untrainables for your amusement?
They care, I have done this and they get bad thoughts from the people starving outside, and you have to produce TONS of slabs to keep your fort from swimming in ghosts.
A starving dwarf had better be a dead dwarf.... you have to TRY to starve in df thanks to above-grounds all year planting season. Hell, if you bought seeds every season you could probably keep an entire fort fed with nothing but cave wheat or sweet pods.
As for OP's other questions, they need to form a relationship to get pregnant/married so you should be set.