All these remarks seem Well thought through and are about Heat,materials, danger,...
But not much about growing.
Here is my thought,
In the current design, there is only glass to the South. Wouldn't that get the plants growing to the glass? Stretching for light (especially in the back?)
The main goal is to grow year round right?
IT would be a shame if You get the right tempetature but the plants dont grow well because off "wrong" light.
Strange Idea: some mirrors on the back wall?
Appart from that, verry interested in dimensions as i dont have much room in my garden (7meters wilde) and migt try this in the future...