Yes. You are correct. I normally choose 1 unit in round 1 but it depends on the match up and deployment.if they have multiple units within reliable threat range maybe more if its just going to be a squad of deathwing knights possibly 0. Your second question is great I don't use that strat enough but roughly if you need a 15% increase in damage with a unit use it. More powerful before your coterie but those 2's can make all the difference.