This is a good instructive video and with three burners, the forge should produce a very powerful heat. I should like to see how hot you could get that spike. I have a commercially produced gas forge, which was expensive to buy and more expensive to have serviced. Even with an insulated door shut, it is uncomfortably hot in proximity. Whereas with coke, I could hold an 18” bar, it rapidly becomes impossible to do that with gas. But it doesn’t burn the material.
Did you research health risks associated with that insulation? Cutting open a gas tank is risky unless it’s steamed out, I hope you made that clear. We cannot buy cylinders like that here, they remain the company’s possession.