You could do 1-2 and grow them larger or 8 smaller plants.
So 1 for one of your size bushes possibly larger depending on stain or 2 smaller than yours il have to see what sort of yield you get how many autos could I fit in if trained but not being to small you reckon 6 would be a good number for average-small autos? Bare in mind I won't be using as many watts as you as I don't have that kind of money or legality over here to be risking the electric snitching my electric bills up lol