Whose VO? Barn: "You know how the Devil makes work for idle hands? Well, he will be busy." Not sure whose hands. I thought Barn was going to say, "Well, mine will be busy." I decided it was Trask's.
Maybe attacking Trask gives him validation as the good guy of the "story". It's also a way of working off some of that evil vampire energy without hurting innocents for awhile. I think it shows the vampire instinct eating away at his former human self, half wanting to save Vicki, half more concerned with premature (she isn't dead yet) revenge, than with stopping the execution, which is not totally impossible given his powers.
Barnabas can just turn and look at the nearest candle and speak, in order to cast a spell! Unless he was just talking to himself about his plans to do in Trask, right after Ben left... in that case though, why look at the damn candle?! Why play Angelique's spell music? Did Barnabas learn this one from that wise Carribean Indian on a business trip, then forgetting he'd ever believed in witchcraft by 1795?
Farewell Maude Browning, almost, sort of!