Just to add that the various Prospector things (LNP/DFHack tools) can probably tell you what
can be found (but I couldn't tell you what the exact method of doing that is).
If you need iron, you need those iron ores (or possibly take dribs and drabs of smeltable ores or meltable items from complient traders, but that'll be slow). If you want steel then you additionally need the flux stones (and/or a trader source, and/or steel things to melt) - that's more or less the steel industry, if you ignore bessemer converters and such...
Non-ferrous metals don't need the flux, just the particular raw ores/meltables (of all necessary types if you're wanting the derivative alloys) and copper could be a reasonable fall-back of last-resort (I've rarely had
no copper ores) though can probably be improved-upon for various different purposes when you find other non-ferrous resources. There should be a full ingredient/product flowchart on the wiki (or it's explained in longhand text), and that or the weapon/armour pages should be able to suggest good/better/best rankings for various weapon types and armour, based on in-game density/malleability/etc vs what is best.
(There are also 'tricks' to take a small amount of metal and magically expand the resources, but get a hang of the basic industry first, because it's more useful in general.)