Hi there, its great youre looking at building a greenhouse to keep your animals, and push the envelope both in building technique and climate. While I like the wofati idea, i have some reservations that it looks like youre addressing which is great. PAHS is great and if it works its nice to have free heat and cooling, but i liken it to flying a fighter plane without an ejector seat, its on the edge and if you have no safety net, it can be bad.
As far as the depth of insulation at the top of my head i dont have any data on it, but i have seen something similar on another websites earthship forum about them using insulation below the frost line in scandanavia, so it makes sense on an intuitive level that youd want a thermal enevolpe that doesnt give heat back to the earth easily but has earth around to buffer the cold wind, etc.
Id look at geo-solar, Geoff Lawton did a video on a greenhouse in canada using it, id look at having the tubes blow that warm air back down into gravel contained in your thermal enevolpe instead of directly to the earth, it might be a bit warm in summer, but all that warmth will be held more for use in winter. Its an expense in the beginning but will pay off quick and is passive. Next id look at a rocket mass heater, its not passive, but its as close as possible for an active system, uses little wood and if something isnt quite right, you have a heat buffer that might someday save your animals in winter.
You might add solar hot water, or extra solar air heated "wings" off to the sides, a popular one is the aluminum cans painted black in cells, but im not an expert in them, maybe theres something better out there now, you could blow that warm air in winter and it wouldnt cover your main greenhouse windows.
If you have enough heat in winter you might check out some aquaponics systems to grow forage for the animals, plus you can eat the fish and grow veggies for yourself too
check out the book solviva for a neat example, good luck.