also, dont be afraid of putting some early copper or silver traps down. In fact, silver is great for spiked balls, and copper or glass does decent for serrated discs in the beginning. Dont be shy to make a cage trap at the end to capture the captain, who is usually the strongest and may be able to dodge past any traps
Dont put too many weapons in one trap. It can block and then you dont have anything anymore. As soon as you find tetrahedrite or galena, you can make copper/silver things. In the beginning just burn some wood to charcoal, done.
For traps, consider this: discs have a hard time penetrating anything of better quality or material, but are devastating against unarmored opponents. The goblins may not be struck in the head or torso, but it'll be raining arms and legs, even when its just glass diss. Trolls already have a tougher skin, so, plan B
Spiked balls are not exactly killing weapons. Only a lucky strike to the head or the chest at the heart has a good chance. They are however excellent at disableing. Copper is decent, silver and bronze good, bismuth bronze ideal for this weapon. The blunt force impact ignores most armors and breaks bone half the time. When its the second toe of the right foot, thats not too important, but in the end they will break almost every bone in a body
menacing spikes do mostly internal damage, tearing guts and arteries, as such they can quickly kill, or be useless, it really depends. They do have a chance to sever limbs, but less than other weapons
Giant axe blade is basically a pumped up version of the serrated disc. However, the disc has 3 attacks and the axe just one, making the disc more powerful generally speaking
screws can be used in traps too, but i never have, so no opinion there
weapons:
putting normal weapons in traps is a good way to use loot from goblins that you dont want to smelt down to bars and dont want your militia to use. A weapon trap with whips and scourges is pretty high on my list to avoid running into. Similarly, large knives can be deadly even in quite unskilled hands, but you might want to stick to more traditional weapons. Putting them in traps is not a bad solution
Note that half of my traps will damage but not kill, if i want it that way, so you'll still need some militairy, possibly. Mixing different weapons in one trap will make it more deadly in my opinion. Make it whatever way you feel comfortable and note that many people say using too many traps make the game boring
so yeah, i'm quite good at traps, less so at training a militia, someone else may help there