I would prefer to have the t-stat control the hot side of the tank, because to my way of thinking, getting too hot is more dangerous than getting a little too cool. But that's just me, others may think differently. If your temps are already holding steady with both rheostats, then it probably doesn't make a huge difference where you plug the first t-stat in.

As for the night drops, you don't need any. Just keep the temps the same 24/7.