a rheostat is basically a light dimmer. I picked up one at a large hardware store(Menards) and it plugs into a wall socket, and then you can plug your electrical device into the rheostat. Mine is a sliding light dimmer type.

I have a thermometer/hygrometer combo that measure the ambient air temp/humidity levels, and I have an infrared thermometer gun for measuring substrate temps.

Yes you need to leave holes for the lights and ventilation.

hope that helps