I will be at the event 90% of the time. I suggest considering a trip to the military equipment museum in Verkhnyaya Pyshma as an alternative to the Yeltsin Center – it's the largest private museum in the world. There are also retro cars there, and it's not far from the base.
For locals, perhaps there's an option to arrive/depart instead of staying permanently? Although there are also advantages to staying.
I support a vegetarian menu.
My primary concern is the number of participants who will be staying overnight.