firstly Birroc... i definitely dont consider myself an expert...... i most definitely do not know everything, i only give opinions and try to base them on experience or trusted second hand info..
My profession demands me to know a significant amount about a lots of particulars in construction...... i dont specialise in any particular aspect, my job is more of a gathering of info and augmenting this to suit the build.
personally i would go for SIP panel walls and roofs with battens cement board and finish.
I would install the new nordan windows that have double glazed at u value 1.2 and triple glazed at u value 0.7 !!!!!!1111 budget permitting of course.
If i could get the construction as close as possible to passive levels i would design a solar collector space and water heating system, with possible on demand combi boiler for those coldest winter days... and that would be for hot water only. i wouldnt allow hot water to heat over 50deg.
Its important to understand that if you can trap heat as well as you can within the building envelop, then it really doesnt matter how you heat it.
A HRV system is a necessity....
Of course all this would need a fairly extensive budget