You can buy all the steel junk from dwarves, do top request for flux stone and steel bars, and that will get you some small amounts from the dwarf merchants. I've found that with all my other requests levels down to just one notch, I can get 5 flux stone (marble) per dwarf caravan. Man, that's when you miss the wagons.
You can buy bronze goods off the humans, and melt that down to get bronze armor or weapons. Bronze is better than iron for bladed weaponmaking, so that's something.
Silver is your BEST bludgeoning weapon material, so make all your war hammers and maces out of it. In fact, if you have galena, you should have lots of silver available. Just outfit your early melee dwarves with silver hammers and whatever armor you can muster. Outfit them in iron if you can get that going quickly, and then replace the iron with bronze and steel as soon as you can. Should do alright. But your first bronze should go into battle axes, so you can get some militia that can chop off arms, legs, and heads.
Personally, I prefer to defend my dwarves through architecture, and only have a melee squad for beserking dwarves or visitors. Melee squads can be useful to go slaughter bothersome animals that disrupt the civilians due to their location, so I will often employ them in that capacity as well.
Since I know how to get my crossbowdwarves to get bolts, I prefer to have a squad of those around to shoot goblins that are hanging around my goblin grinder, so my fort can hurry up and get back to normal day to day business.