Good luck az. What type of tank you going for ?
Do you have a sump? move the thermometer to the sump... eyesore
If MH lights are causing temp issues you may want to look into LEDs... run much much cooler. (not saying better, just cooler)
I like the 2x pilers of rock, however you might try to stack them "looser" (i.e. more room for water flow between each rock).
I might remove the center rocks... but thats just me.
IMO you should run all three bulbs. How many bulb setup is it?