You no longer need to worry about the thermostat as the Ranco is now the thermostat. I just set mine to about 3/4 of full power and left it there not exactly knowing what else to do and it works fine. I haven't had to play with it.
Basically, the Ranco detects the temperature from the probe and turns the fridge on and off accordingly. Just plug it into the power strip, set the temp on the Ranco and you're good to go.