Protip: when traders are at the depot, you can use the search function to find all of the Narrow Iron items that haven't been gathered up yet, and designate them for melting/dumping/forbidding from within the Move Items to Trade Depot screen. I
long for the day that this feature will be available in the (Z) Stocks menu!
You can make armor stockpiles only have stuff that are usable. Just press q, go over the armor stockpile / weapon stockpile, and press u or j. It'll make it usable items only, or unusable items only.
You can even do things more granular than that. I typically like to have the following piles customized for separating Goblinite from useful armor.
Bins as Currency (these piles go near the Depot)
Because these piles end up with a pretty predictable mix of items, you can count the bins in each pile to get a guesstimate of how much you can afford to buy from the caravan.* Unusable silk armor and silk finished goods ($4k - $10k per bin depending on GCS frequency)
* Unusable leather armor and leather finished goods (about $100 - $300 per bin)
* No-modifier wearable leather armor (about $200 - $500 per bin, higher if you've been importing fancy leather)
* High-modifier unusable any-metal armor (rare drops from goblin bosses, usually no more than $2k sitting around at a time)
Goblinite Ore (near smelters)
* No-modifier unusable any-metal armor, metal weapons, except for whips, scourges and metal shields
When a Problem Comes Along...* Iron whips and scourges
(I use captured whips in my "safety" weapon traps behind my main entrance. I prefer them for the gore damage - goblins wracked with pain are easy pickins for even the most inept recently-drafted cheesemaker)The Delicious Steely Fruits of Dwarven Labor* Low- and medium-modifier wearable leather armor (near Dining Hall, for emergency militia drafting)
* High modifier wearable leather armor (near Barracks)
* High modifier wearable copper or iron armor (near Barracks)
* Masterwork wearable armor, leather or metal (in a separate lockable "dressing room" near Barracks)
* Masterwork and Artifact Weapons (in a different, separate lockable room near Barracks)