Thanks for the (very nicely presented) information.

"metal and hempcrete should not directly touch as it encourages condensation and eventual weakening of the hempcrete over decades. "

Brings to mind another easy overlooked fact.
Oxidation
Take note of the galvanic series when using screws on metal.
Some combinations of the galvanic series DO speed up the oxidation process.
Avoid mixing these.

Thinking of metal,
A Faraday cage could be a nice addition to this nice house.

Cheers