That is going to be a massive and heavy pit...I hope all these events are at your house cause moving it is going to be a chore. With that said, I had the same idea and ended up marking a pit too big for my back yard. It's too heavy with my big warmer box and that same warming box/vertical is never used since I don't cook for 300 in my backyard. It's got a lot of great ideas but make sure it fits your needs.
My only other comment is that you are going to spend more hours boxing in that pipe and fighting with shelf placement that you might be money ahead building a square box from sheet metal. Easier, faster and more compact. But yes, it means a full sheet of plate.