I'm fine with my long sleeve jersey and shorts until I hit the 40s. Won't bother with long tights until I'm guaranteed to be in the low 50s or less quite a while. I overheat quite easy, even a light shell jacket will keep me fine down to about freezing. Tights and a softshell below freezing.

But, it is personal. I am very cold tolerant. Get me up to 85F, and I am suffering.

As far as acorns, my 32mm+ tires aren't bothered by them, haven't ran them over on skinnier though.