I'd like to point out a couple things:
This greenhouse is 6 x 8 ft, where are you putting all this stuff?
The air temperature for orchids is important, not just leaf temperature. You will have to keep the air temperature in the entire greenhouse at between 75F (nighttime) and 85F (daytime) winter and summer. Radiant heat won't work unless it has a fan - only things close to the heat source will be warm and they will be really hot, not just warm. Radiant heat is very zonal - how will it heat the part of the plant behind the rest of the leaves?
Propane gas byproducts kill orchids so your heat will be electric or kerosene. It would be nice to warm your greenhouse with sunshine but how much cloud cover does your area get in the winter? Your greenhouse is not that well insulated.
I looked up the specs on your greenhouse and I'm a little concerned. The snow load is 15lbs/ft and wind rating is gusting to 56mph. Snow is heavy, it weighs over a pound per inch. I'm concerned you will have a crushed greenhouse in the first big storm unless it has blown away first.
