Ah, I didn't see that in the first photo.Ok, the one on top is the heater.View attachment 157474
Do I need holes on the lid or keep it completely sealed?
Your question is probably for the more experienced than me regarding holes and air flow.
However when you put the lid on it should naturally let some air through replacing stail air.
Others will have way more knowledge on this than I.
@Tom @N2TORTS should be able to help with homemade incubators. I'm guessing they have played about in earlier years.