Mystic Forge Salvage Kits Questions...
3 Mystic Forge Stones, not coins. You can get them randomly for map completion, I think from Black Lion Chests, or most readily directly from the gem store.
Also, you can check the wiki to make sure of a recipe, and yes, they have to be unused kits (they list durability, not amount, you can’t split them into separate stacks, etc)
They have to be unused, but ultimately you’re plating like 25 silver for a salvage hit that has 250 uses.