Try all the "crazy" ideas. Some will help, some might not. I've been trying unique things out since 2016. Some have worked; others did not. It's a learning experience and part of the fun of owning a greenhouse. You are always tweaking. Creating removable panels with bubble wrap in between would definitely create another air space of insulation.
I also looked into those Chinese roll ups, but like you could only find them for very large greenhouses. It would be nice if someone offered custom sizes. I have seen, don't remember where, frost blankets that you can hang inside and draw closed at night.
Wood is a good choice. I've heard of many people successfully keeping their greenhouses heated with wood stoves. The only problem with wood is you have to tend it, and on a real cold night that may mean getting out of bed in the middle of the night to stoke the fire.
You will definitely need supplementary exhausting during the hotter months. In my old greenhouse I only had two roof vents. Luckily, I also had a front and back door that help ventilate the greenhouse. This new greenhouse has 4 ceiling vents, a front and back door, plus I installed a 20" exhaust fan with a 24" intake louvre that can change the entire volume of air in my new 280 sq ft gh in under a minute. In fact, I just covered both yesterday with insulation for the winter.
