I have read that most nursery people cut the taproot from oaks when planting
to encourage a more fibrous root system. I don't know if I agree with this
or not but I would assume the taproot is only important in areas with low
rainfall or very windy areas?

I have also read that planting in the fall is best, especially in my neck of
the woods because summer drought and heat can be stressful on a newly
planted tree. In the fall, the tree would have time to put out new roots
and settle in before cold weather and would have a head start for spring.
However, I have also read that plants in pots can be planted at any time; I
guess it just depends on your climate. Since you have more than one, maybe
you could experiment. Good luck.