I take the feat. It adds to AC quite normal outside sombat, but that +1AC sometimes is lost during combat...
Yes, but sometimes you do require the loots to continue the story, like that lamp on Nere.
Well on Patch 6 it seems the bonus action for great weapon master, i.e., when you strike down an enemy can be reserved till next round. So you may jump, kill someone, and strike twice for your next round(1 normal action, 1 bonus action which is passed from last round)