As others have said, skill is so much more important than materials, especially dodging and blocking skills, because it means your dwarf will survive hundreds of dice rolls and counter attack over and over. Even if you're using a copper axe, it can still do blunt damage if it didn't pierce their iron armor. Most vanilla monsters aren't fully armored anyway, so you'll score plenty of hits on unprotected parts of their bodies. Secondly, the material that you use for bolts isn't very important at all. Silver bolts are the best, but copper bronze iron and steel are almost exactly as effective, so just use whatever is cheap and available to you. The material for a crossbow is not important at all unless your marksdwarves are in melee range using the hammer attack. Finally, maces and hammers use blunt attacks, so silver is equal or better than steel, and any dense material at all makes a fine choice.
In all of the above cases you want to focus on crafting skills and combat skills first, and then materials second. Steel weapons and armor ARE better and it is an enormous advantage to make your armories out of it, but at the same time it's very hard to say what the difference is between a low quality steel breastplate vs a masterwork copper breastplate. Or a masterwork copper mace vs a low quality silver mace. But assuming that everything is masterwork then of course go for steel and candy.
I wouldn't stress about iron and steel on your embarks (though you DO want the flux). I think the only requirement for a good embark is copper and a flux layer (marble!). With only copper you can start training up weaponsmiths and armorsmiths immediately, and if weapon/armor smithing is their highest skill then later on when they have a Fey Mood they will make an artifact weapon or armor (fully customisable by you, by the way, if you forbid certain materials when you get the Announcement then you can force platinum weapons or steel armors if you want).
You don't need iron on your embark, you need a melting industry. Get down to the magma and start melting and forging and melting and forging as soon as possible. Melt everything that isn't a masterwork, melt the goblinite, melt all the crafts you buy from the outpost, ask them for steel toys and steel crafts and steel bars. You can even utilize a few duplicating tricks if you want to, put Forge Giant Steel Axe Blade on repeat then melt them all down to quickly get 1.5x bars you started with. If you feel bad about duplicating then don't.
Asking the Liason for steel and iron jacks up the prices, and importing all those steel weapons and crafts is actually VERY expensive considering some things like a decorated flute can cost 5000 and a giant spiked ball could be 8000, so if you want to buy out a caravan it takes more work than just stonecrafting on repeat. It adds a nice element of purpose and challenge to your crafting, you'll need more things going on simultaneously like bone crafting, jeweling, and silk cloth. Don't cheese it with masterwork cooking though!
If you can reliably get that magma forging up and running in your early years before ambushes and seiges, then you've like quintupled the number of "good" embarks out there. Instead of focusing on the metals (you're happy with tetrahedrite, remember?) you can focus on the terrain around you and get other limited resources like featherwood trees, fun zombie biomes, sand/clay, volcanos, glumprong trees, and most importantly you can more easily and happily choose an embark area that you just like asthetically.