If I've got two weapons, one has +Life on Hit, does it only give life when that particular weapon hits, or when either weapon hits?

If it is by weapon : I've got an amulet and armor that also give +Life on Hit, are the values from these 2x as valuable as the weapon bonuses because it counts for either weapon attack?

Same questions with +Attack Speed%

As a Wizard with primary stat of Intel, is a weapon with 1000DPS and no intel better than a weapon with 800DPS and 200 Intel? Whats the formula for it?

As a Wiz with Diamond skin, does it do damage to the HP Shield created by Diamond skin prior to damage reduction stats resistance and armor or after?

I'm sure I'll have more but lets start with those.