I doubt that 4 vs. 5 vs. 6 is going to make much difference in their perception.
But 6 is a much better number if you are dealing with minimum orders from hatcheries, and I see many threads claiming that Tractor Supply will only sell chicks in quantities of 6 or more (I do not know if this is a policy of the whole TSC chain of stores, or if this is per-store or per-state policy. Some states do have laws requiring that young chicks be sold in quantities of 6 or more, so that is probably the cause of TSC's minimums in those states.)
And if you have adult hens and want to raise new chicks, two hens plus two chicks makes four, and that is the bare minimum for each hen and each chick to have a same-age companion. If you have three older hens and get three new chicks, there you are at 6 birds again.