Brian, how exciting!  I can tell you have put a tremendous amount of thought and work into it.  I really like the greenhouse you've chosen, when we bought ours the options were pretty limited, not many styles between small home gardener and professional. 

I'll have to go back and read through this thread more thoroughly. 

My plants are all in pots, although I've cut out the bottom of some pots to let them root through into the ground, after they took that route themselves, through the holes in the bottom of the pots.  The Ceiba and a few cactuses grow this way, some of the cactuses are at the edge of the greenhouse so I worried about them getting cold feet.  My guys did not do a good job on the base, it's basically a wooden wall with a little insulation tacked to it. 
I can feel that the bottom of the gh is cooler, but it hasn't seemed to affect anything so far.

Hi Brian,
I'm late to the discussion but I have a 21 x 36 Natural Greenhouse that you were first looking at.  We like it quite a bit except for some minor drawbacks. 
1).  It's big.  I made a mistake calculating, I looked at the plants in our house (8ft ceiling) and then decided to go with the 8 foot sidewalls.  Our land wasn't as level as I thought, so they had to build a wall for the GH to sit on.  So, it is TALL.
2) We put it up ourselves except for the initial wall and most of the roof polycarbonate.  We finally rented a cherry picker and some handymen and it was very easy then.
3)  It does cost a lot to heat.  I don't remember what we kept it at the first winter, maybe as high as 70, but it cost $2000 for the propane.  We put in a wood stove that does most of the heating now.  We get 1 tank load a year, about $500 depending on prices.   And no, the stove does not affect the plants at all, although they did get a bit sooty at times.
4) The inflatable sidewalls work great until they don't.  The back up batteries do fine for about 2 hours, but you should have a generator just in case of longer power outages. 
5) Invest in a concrete floor if you can.  We live on a rocky clearing where there is no dirt or grass, and a lot of dust.  The dirt floor of the GH also makes a lot of dust.  This gets on the inside vents, walls, and parts.  We've never had problems with the 2 fans, but we have had blowers go out.  My husband was thrilled to replace them at 2 am with snow coming in the vents.  And yes, the plants were fine.
6) If you have regular breezes, the natural ventilation works great.  We get very little wind here and in the summer the greenhouse is super-hot, even with all the vents and doors open.  Having grass around the GH would probably help a bit with that, too.   

I've tried to load a photo but not sure if it will go through.