For flock harmony, especially with multiple roosters, the standard is at least 10 hens/ rooster, regardless of whether they are LF or bantam.
For breeding purposes, like if you are separating out one rooster and a little harem and you plan to hatch the eggs and want to guarantee fertility, they say 5-6 hens/rooster.
With three hens and one rooster, keep an eye out for over breeding, loss of feathers on the back, or the rooster harassing them. But if they're getting along, don't worry about it.