I an not sure about the sprinkling system. I like to have someone come by and water the orchids at the pot level and a sprinkler (without lots of air movement) could cause more problems that it would help.

About the extra door versus an exhaust fan. Go for the fan. The door alone is not going to increase air movement that much and a fan will pull air across your orchids and the heat out. JMHO

I am so excited for you!!

Cheers,
BD