OK, I will try and point out the main problems. How you deal with them is up to you.
1) The heavy casing will absorb and hold heat . It will get HOT! Sorry to say, but there isn't much to do about this problem.
2) The brick is the wrong type ( if it is hard firebrick as it seems to be). I would get a steel shop cart from HF and place the hard bricks on the top to make a refractory covered table top. Place your forge on this. That way you can roll the forge to where you need it, and the brick tabletop will help with the heat problem of the heavy case. It also gives a good place to set hot blades and tongs.
3) The right bricks are the soft type K23 or type K26 firebricks. You can use them to replace the existing bricks, and it will help a lot. An inner coating of 1/4" of satanite will make them work better. A coat of ITC-100 over the satanite will make it even more efficient. Because of the heavy case, I would recommend this setup. If you are set on keeping the existing bricks, then I highly recommend building up the inside corners and applying satanite and ITC-100 over them.
4) The steel sliding doors are the wrong thing. Remove them, fill the back with two firebricks, cut a hole in the bricks to make a rear port, and use some of the hard firebricks you have to stack and block as much of the rear port as desired.
5) The front entry port is usually around 3" wide by 2" high. I would remove that steel port entirely. Then you can be adjust the size opening by positioning some firebricks on each side.
Other concerns:
Because the case may get hot, you need to keep propane hoses and electric cords far away. I would pipe the burners in 1/4" pipe from at least 24" away from the forge. Put the gas valves at the end of the pipe, not at the burner end. Hopefully, the shell won't get so hot it causes problems with the burner operation.
That thing is a beast. It will be heavy, so consider stability and such in placing it. This is where the larger shop cart is a good idea.
https://www.harborfreight.com/16-inch-x-30-inch-steel-service-cart-5107.html
Two burners would be more than enough for that forge. One good blown burner would probably run it OK.
A round chamber, or one with curved corners, is far more efficient than a square/rectangular one. Before adding the Satanite coat to the bricks, first build up all four side corners so there is a curved ogee from bottom to sides and sides to top. Mix up some fairly thick satanite for this build-up. Then apply the final 1/4" satanite layer, followed by the ITC-100. Read up on how to apply ands cure these products before doing it.
All the materials you need, as well as lots of FAQ info is on hightemptools.com . If you had spent some time there before your build, you would have seen many forges and ideas, as well as how to properly build a forge. BTW - The stickys in Shop Talk have a whole section on forges and burners.
