Thank you for the sincere answers!
I am residing in Busan, Republic of Korea. So I have some trouble with acquiring materials that are common in the USA.
I asked about insulation to insulation material company and they told me to use combination of fire bricks and silica board.
Goods, I will try to change or think better method to open the door.
Frosty, I fixed my design and I've attached pdf file of my plan. Did I solved major issue?
Thomas Powers, I designed my forge to be portable since I can't stay in my current workshop too much. If I can found cylinder that is equivalent to 10" auger tube maybe I'll make simple forge first.
George N.M., Thank you for your suggestion. I'll research about it.
About the over design I chose hexagon to have stable brick placement and strength. Also, as mentioned in reply I have to make my forge to be portable and easy to store.
Lastly, this is definitely overdesigned but I wanted to make modular forge. If this is terrible idea I'll just stick with single forge design.
Again thank you for your comments!
HEXForge drawing.pdf