Ive been recommended with 6 as well x What bottle size are you getting as i have been told to get the small like 160mls bottles for the first months?
With my first I had four of the bottles that went up to 5oz and when she started drinking more I had seven of the 9oz bottles, the sterilisers hold six bottles at a time so there was always a spare bottle
I'd say 6, first time round I had 12 and then got lazy with washing them so had to get rid of half so minimum I'd say is 6