I had a meeting with Mike, an Architect-Builder friend who was one of my tutees years ago, who I would trust to build it. We discussed the idea of building the SIPS panel ourselves, as a summer vacation project.
I've also written to AnafSolar, volunteering to instal two of their panels on the roof - as an additional solar heat supplier to my ground loop. It would need its own energy flow meter, pump and thermostat.
I've been skyping with a friend who works for Rationel, a high performance Danish window company with a base in Bicester, Oxon. The South and East window will be triple glazed, argon filled, of course. The SIPS walls will have a U Value of 0.15. The window will add to the heating gain, because it will be clear and intended to admit more heat than it loses (and there is a solar shading device for summer).