AFAIK the armor sets are not random. They're not in the same place in DKS as ED, but not random. The other items are procedurally generated so they will vary. Some armor pieces require you to complete optional puzzles and locate hidden chests.
The best way to get a weapon is to find the weapon with the best base stats. Personally, I've found the best items at vendors. This is especially true in FoV where vendors are selling named (gold) items with ridiculous stats.
Next look for weapons that have good enchants on them. Early on you won't have many opportunities to pick up the enchants themselves so what you can do is disenchant items that have so-so base stats but awesome enchants. Disenchanting a weapon allows your smith to learn enchantment. You can then apply the enchantment to another item.
Malachite is used for the top tier (Level 10) enchants. You should always keep as much malachite as possible. There is a limited amount of malachite available in the game. If you are presented with an opportunity to buy it, always do so. However, its less important once you reach FoV since there are many more opportunities to obtain malachite.
