Cooking for a crowd is something I usually botch, but here are my suggestions based on those botches!
I would build the fire across the entire diameter of the big joe, and bring it to 400 degrees with lid closed. As you begin cooking you'll be opening and closing the lid frequently and all that oxygen will drive your temps even higher. I would not use heat deflectors. Lid closed except for when you're flipping the burgers, putting on cheese, etc. If you leave the lid open the fire will get away from you. Cheese usually melts in 60-90 seconds under these conditions for me with the lid closed.
Be glad you don't have a griddle, if you tried to cook that many smash burgers the amount of fat rendered would be unbelievable and would make cooking very difficult IMO. However, if you have grill grates you could use the flat side as a griddle and the slots would take care of the grease build up.
I hope this helps and good luck with the cook!