I have 8 rubescens peacocks that I got last November. Since then only one has colored up and all the rest are female. They are all about 3.5 inches. I would like to encourage some breeding but can you have too many females for the male?
IMO you can't have too many, but at a point you probably don't "need" anymore (which would depend on conditions - tank size, fish purpose, tankmates, etc).
I've noticed when some of the larger breeders/distributors move out breeding groups it's typically 1-2 males and 8-12+ females.
Another observation, from a breeder perspective the females are worth more than the males, while to a hobbyist, a colored-up male carries the higher price tag.