remember to insulate the combustion areas
beware of dangerously high temperatures
use appropriate materials
refractory materials can be insulative, or not
p.s. as a last thought, I'd recommend everyone build a "tin can rocket stove" for cooking on before attempting anything more substantial,
here's a link to a page that will assist you in building one, with all the appropriate reinforcement of basic concepts
Here's a publications page from a major heating vendor that contains a LOT of information about hydronic heating systems. No. 10 on the list (displayed latest first) specifically targets wood heating. They sell "modern" technology but the principals they discuss apply across the board.