I wrote a reply to this but maybe it was the day permies was sort of down and it didn't get posted, I don't know.
I've lived in houses heated only by attached greenhouses for the past 20 winters. We get a lot more solar gain than you because we're only 34N, and high, dry, clear and sunny. Our Jan minimums tend to be -22C or so, ie a lot warmer than yours.
I think that its great to have your south wall exposed only to the milder wind free cold air of the greenhouse than outside.
Eliot Coleman's
books have great info about getting the most vegetables and season extension out of your greenhouse. For example a lot of salad crops he grows to size in fall and lets then stand there fresh on their
roots for harvesting all winter, even if they don't actually grow in midwinter. This year I followed some of his variety suggestions and it has been GREAT! I had fresh greens every day of this winter, when there hasn't been anything fresh in the market in our region since December when the highway closed for the season.
Two questions. It looks like warm air circulation into the room is only those slot shaped openings, is that right? We have nice big windows and doors to open when greenhouse is warm and close at night. We get a lot of heat gain in the house from this.
Secondly, I'm dubious about heating beds by piping hot air from the top of the greenhouse. Hot air has so much less mass than soil that piping hot air under cold soil might carry negligible heat.
For keeping grow beds warm, Coleman recommends adding covers over beds or plants inside the greenhouse for the coldest months. I don't need to do that because my greenhouse only drops to -5C at worst, and all the leafy greens don't mind too much.