depending on the power chord the strum would be strings 6 & 5or strings 5 & 4

no more strings so no more notes added ,keeping the chords as power chords. 

Generally it would be stay with a lesson until understgood, move on to the next ones but keep looking back and decide what skills you wish to build in to a practice session.

This session will evolve as you do more and maybe decide a direction or maybe just recognise some weaknesses

Dave