A company I have worked with thru my insulation business has done a lot of marine insulation. They use polyureathane foam. It is an extremely good insulant. Timber framed houses are tricky to insulate. You can use cellulose insulation within the inner cavity void formed by the timber studs if there is one. Then there is draughtproofing which is not particularly difficult nor expensive but more of a labour of love to find the draughts.
For the heating there are some sensible suggestions here already.
I would add as a possibility for the wet heating system a water source heat pump. Typically you might place a radiator-like device into the water. https://www.nuenta.com/viewproduct.asp?pid=109 it would absorb heat from the water.
But here I wonder whether one might actually use the hull as the heat collector by running pipes round its inside.
It would be an interesting project and should in theory qualify for renewable heat incentive support!