I to am in the market for a thermostat. I think I am going with the Herpstat ND. I am going to email the company soon and find out 100% what model I need for use now and possibly for expanding down the road. Right now I have 3 enclosures set up, but not all running as I only have the one BP. (I just got the ball rolling, plans on expanding are in the works)
I know I dont have much experience with this, and I wish I could be more help. But I will suggest Spyder Robotics, as all of my hours of research leads me to their products. Good luck with your search, hope you can find a good deal!
Cheers!