I assume it works similarly to a Mama Heating Pad cave. If the chicks won't stay in, it is too hot. If they won't come out, it is too cold. If they come and go, it is JUST right.
No need for intermediate holes though operable windows with 1/2" hardware cloth covering the opening are good. Chickens like light and they can be opened in the summer.
Things are usually easier the second time around. Learning is good
I agree. I believe the OP said she read the thread (article?) on ventilation. Better off with bigger openings some inches above shavings/straw/whatever-you-have-on-the-floor level. And similar or ridge vents up top. Some people use operable air duct registers, choose long and narrow. Easy enough to cut the opening with a jigsaw or reciprocating saw. Make sure they are covered with 1/2" hardware cloth on the inside.