The main problem is you rush and pump the Fort Value, Hi Fort value = more commonly ambushes.
Donīt rely in your militias they gonna suck when the first ambush comes, unless they are nearly "legendary" in the skills you already read and you are covered in Steel armor. lesser metals as Copper and bronze are good for random savagery.
You should wall yourself ASAP. And your main gate (and the only one ) should be with some short of trap system, the most commonly used is the "Minecart goblin grinder" and relatively "cheap and fast to build", but a well cage-trapping in a narrow spots, should do the trick at the start (just avoid the dwarves goes to pick the cages too soon before the danger ends).
Your fort door should have some security double or tripple retracting bridge setting.
You can chain a moleweasel or any animal there for lure the ambush, but your dwarves are safe behind the second retracting bridge. force then to walk for a 1 tile narrow path put some traps there like weapon traps, sawblades etc. They for sure are going to dodge, and after they dodge they gonna fall at sides. The stuff under that pit is up to you, fill this hole with deep water and no spot to climb back. If you wish retrieve the goblinite after, you will need do a smart pump system. Other people uses magma for sake of fast cleaning an effectiveness, yo will lose the low melting point goblinite.
The minecart method is a double edge weapon, cause it can hit your dwarves too. So you need a lever to shut off the trap when there is not danger.
Other way is fill this pit with a dangerous animal, likely an trained one than donīt need grass. Like drow spiders or Forrest spiders (you need to buy then from elves-drows).
MWDF have a ton methods to get metals for easy, so gearing your militia plus the guilds, let you stay training fast inside your fort till your have the armor and the training for fight nearly anything. Also poisons, spells...
Btw, if you put landmines into cages, then use the catapult-aim script you can load these cages as custom ammo into them and fire landmines into enemy groups.
This is pretty fancy method to defend yourself but is pretty fun :>