The most efficient stoves are the Russian/Finnish masonry stoves with a typical over 80% use of available BTUs. Properly built, you can put your hand over the chimney and feel only a slight warmth escaping.

They burn very clean - but it depends on the wood and how dry it is. I lived through several harsh winters  with two these at each end of a large wooden house in the forest. They are economical with wood: we had a winter's worth stacked up outside under the eaves.

The easiest biodiesel is locally pressed oil from say rape seed. Your diesel engine will have to be slightly adapted, but it is not major mechanics. It's much easier to adapt an older diesel engine. An old Perkins in a boat would probably burn the stuff as it is.

The building research division of VTT the Finnish state technical research centre was been developing new timber construction techniques. One of these is massive  laminated load-bearing beams that have been used to span 20-30 metres.

You can't be me, I'm taken