With metal armor, it generally goes by historic and realistic values. Coper is a very malleable metal, but it can at least hold a sort-of rigig shape for armor and a blade for weapons. As far as i know quality adds a small bonus to how much it'll stop.
Same deal with weapons.
Gear goes as such
Silver (weapons only; best vanilla DF hammers) < Copper < Bronze/Bismuth Bronze < Iron < Steel < Spoilerite (worst vanilla DF hammers)
Any metal will work better for armor than leather.
1. Quality on armour affects the rolls that affect the chance that armour has to blocking a hit. If it blocks successfully, then material awesomeness takes place to determine any damage (if some at all) is inflicted.
2. Same with weapons, except this affects to hit rolls.
3. Steel is right up there with silver when it comes to warhammers. It's a good, versatile metal. Iron vs Bronze is still heavily debated.
thats really helpful, thanks very much.
any idea about the 1 or 2 weapons question?
Dwarves given a ranged weapon and a melee weapon can sometimes get a bit confused, but for the most part they behave exactly how you'd expect them to - they shoot their crossbow, and if anything crosses the threshold where the Dwarf would rush in and attempt to bludgeon things to death with it's crossbow, they rush in and attempt to bludgeon everything to death with their crossbows and whatever other weapons assigned.