Hi Evan;
Welcome to Permies and welcome to the wonderful world of rocket science!
So, right now before you leave Texas , Get IFB from your friend at the refinery. Even if they have to be new you will still be money ahead.
Same with the heavy bricks If he has them... get some. Split bricks are handy to have as well. You won't find a refinery in N.H.
The castable refractory personally, I would skip and go with Lincoln 60 fire clay and #100 sacks of medium builders sand from Home D for about $11.
As far as cheap firebrick. A large percentage of mine were free. Look for sawmills that have a dry kiln for drying their lumber.
They will have firebricks in the kiln. Sawmill owners go to auctions to buy parts for their cobbled together mill.
Many times they will come home with pallets of used firebrick. Quite often they don't need them so off to the bone yard they will go, where hopefully you can find them and strike a sweet deal...like free!
Now I will tell you that brand new heavy bricks are $1.88 each at our local masonry supply house (Mutual Materials) Fire clay is $7.50 a #50 sack
Stove pipe) Thru your roof
Class A Insulated in a proper roof jack. Insulated pipe outdoors. So yes the outdoor portion is spendy. Indoors all you need is single wall. Depending on location 5' sticks of HVAC pipe can be used.