Two things, if the house had a difficult pitch I would always use the vac even if it was to take longer , but I would have already charged accordingly so makes no odds.
Secondly I have no idea how many pitches as it depends on the length and how full they are.
All I can say is I use 2/3 wet sill cloths, 1 extention pole with right angle at the end, stand off if needed and a bag for leaves