Dcav, Welcome aboard. What do you do in Auto repair?
I do autobody/ collision repair. Working in Auto repair you could practically make a forge from free scrap car parts and being able to weld you are almost limitless in ability to make one.
A couple thoughts, a larger diameter tuyere would probably be better, and a simple thicker grate over it, and raise up your inlet pipe for room at the bottom for an ash collection and dump. (Ash likes to accumulate in the bottom of the air inlet eventually blocking the air supply.) a weighted flap at the bottom makes for easy ash dumping. (I fiddled with a screw on cap way longer than I should have.)
Also the refractory cement is not needed at all with this style design so it's just wasted money.
Another help is to build it into a sheetmetal table to hold extra fuel, workpiece, tongs, whatever.
I like brake rotors that use the internal E-brake ( around 8"diameter by roughly 2-3" deep) because it's easy to cut a hole in the table for the rotor to sit in without mounting it permanently so you can change it out or clean it once in a while.
There is a ton of info on here so sit back and start reading and researching.