there are some very good resources and some advice in the Autofocus Choices thread
there are some recommendations in the eos-1Dx Autofocus Guide
from my experience with the 7D and having read this and some of the other souces, i think the single point and one of the point expansions (don't know how much difference it makes) combined with lowish tracking sensitivity, highish accel/decel, and lowish point switching is a reasonable start
Art Morris points out that for flocks you want to use all points to get the nearest bird in focus. He is offering a setup guide for $40 which has some discussion of the choices
