In D2:ED I collected alchemy and enchantment formula from loot, etc, and only bought one or two. Enchantments can be learned by unenchanting a piece of equipment with a filled enchantment slot (you do not recover the ingredients, though).
The damage shown in the stat window (you are right about melee/magic ranges) is the average of the two weapons when you duel wield, so you need to double that to get your total damage. With lower levels of the duel wield skill there is a significant damage penalty to your off-hand (it eventually gets stronger than your main hand, at level 10), so your average is bound to drop. Early in the game I was more concerned with bonuses (stats, hit points, etc) on the secondary weapon than damage.
Weapon expertise effects are reflected in the damage shown, so differing levels of duel wield, single handed and single handed with shield can also change the listed damage.
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