This is actually getting genuinely aggravating. When the first ambush comes, I am invariably slaughtered to a dwarf. I have zero weapons material; not even copper. This type of losing isn't fun. I just feel like I got cheated by constant bad luck.
Bone and wood is all you'll need. Doubly so if you use a dodge trap in your entrance.
http://df.magmawiki.com/index.php/DF2010:Defense_design#Entrance_designsEmbark: Arrived.
1. Haul all the useless crap to where the fort will be build.
2. Channel a ditch, dig an escape tunnel, remove ramps, floor over escape stair/tunnel
3. Get food production up start digging out the underground
4. Prod wildlife for bones and get wood
5. Make mechanisms, build entrance, build bridges and levers. [3-bridge defense with a double L bend added on is recommended.]
6. Build blocks for fast wall construction. Cage and weapon trap (bone/wood xbows if nothing else) the entrance.
7. Restrain an "Alert!" cat near the entrance in case of ambush. Finish dat wall surrounding the base.
8. Designate burrows so your hobos can scramble to safety.(Set dem alerts Bromalade)
9. Get dem reverse fortifications up! [Facing inward]
10. Arm and armor haulers with xbows so you have additional support. Aaaand a force to buy time while the doctors evac to the panic room with the flood lever.
11. ? ? ?
12. Profit cause if you used the double L bend in your entrance design like you should you can watch the gobbos die from traps and getting ventilated.
You can get by for decades with nothing but bone and wood. Get your underground tree/shrub farm going and you'll only need to leave the walls for harvesting Goblinite.
As for the topic, it seems like increasing the mineral count in worldgen+embarking on multiple shallow metal embarks until we find it is the main way. Until then, copper and bone until candy and goblinite suffice.