Hi Dave
you have put here exactly what i have been thinking and trying to sort out over the last couple of months, I am just about to order SIPs house and passive foundation and the only thing i cant get my head around is fitting batten and render board to outside when there are breathable insulation board that increase U value and are easier to install and the mess render system work on. I have looked at the EWIPRO system and thought it ticked all the boxes i had also liked the Baumit open therm EPS system. i know you mentioned you had some issues below so any advice would be very much appropriated.
Regards Richard