Woah! Great update! Albeit leading to several more questions.
Would love to see more details about making the door, and what do you use to get the plaster color? Is that just concrete pigment?
So when you're talking about air percentages, is that % of CSA of the riser, or firebox, or the calculated base? And what size stock did you end up with for air feed along the floor, as I'm sure it's a standard stock? And the primary air and the sheet flow at the door are the same?
It seems like it's a great system. Even though you're not measuring for it, with the reduced velocity you must be cutting the omnipotent PM2.5. I'm not sure it would make sense for me to convert my stove again since it works fine now, but maybe down the road I could add a bigger bench and it would make more sense. I'm really seeing the best application for me to be an oven (finally, one of my own). But this would still be a balance between playing and necessity.
Oh man, and that wood caddy/rolling seat is the bomb.