Your questions aren't related to Tier 5, simply the explanations to a few of the attributes that Shadow Hunters have.
1) light armoured humanoids are any that are wearing leather armour. That usually means mystics, but could mean Rangers also. I don't know how that would be applied to a Ranger that is wearing some leather items and some chainmail items.
2)Yes, headshot can be used in conjunction with volley. When you attack your first opponent, headshot can be used, and then volley gets activated to hit the other enemies in the same round - but headshot only occurs with the very first shot of the battle. Headshot damage will use the base attack of your weapon as a baseline - not the volley damage, because volley hasn't been used by the time Headshot is activated.
I don't understand why you stated your aversion to attacking beasts. It has no bearing on your questions