Super cool. I'm just using a portable, cast-iron forge and hand-crank blower now, so this looks like a dream to me.
You said you would change to make hearth opening smaller. How wide and tall is it now? And what do you think would be better? Are your ideas on that based on the problems you have with the draft, as you mentioned? Or are they based on experience with friends' forges, that perhaps you liked better than your own?