Barrel style oven made of 304 stainless

[Shumate13]

So I picked up a stainless Pig cooker that someone had fabricated but never finished the 1/2 round pieces measure 42Lx33Wx14H I have solid end pieces to tig weld both halves into 1/2 moons and an 8 inch flu stack to tig weld on my plan is to fire brick the floor rockwool insulate the outside then vermiculite and refractory cement over that. My question is how big should I make the front opening and are there any issues that I might be overlooking as this is my first build thanks in advance.

[Shumate13]