Hehe, good, I was just gonna suggest something similar. Mercifully DC temperature and fan control is relatively simple electrically and there are many options out there. Icecap makes a 120mm DC fan with temp controller and thermistor built into it for a mere $20some. Too bad AC motor control is so complicated
Back to the subject the atc800 is a great bit of kit not only controlling the fans but also the heater and there tried and tested just dont forget to set the stat on your heater higher than you need so the atc switches it, i suppose it also will stop the heater if it sticks on as your cutting the power to it and if the atc goes wrong the stat on the heater kicks in
I've decided to copy you on this one - ordered the stuff for it last week and it's arrived today! I'm looking forward to getting it all hooked up and getting it going! No cooling as of yet but I'm going to get a chiller before [if] it gets warm next year so it'll be good to be prepared.
Good job!