4. making it free.
Not to mention if you're using public property you can't really charge them to play anyway...
You will need safe zones. If it's multiple days, people will eventually need sleep. How night games can be fun, and are obviously part of this. You can't expect everybody to sleep with their goggles on, or even expect the goggles to say on all night. Keeping this and charging stations in mind, my suggestion is actually quite pricey.
If you create a barracks for both teams, and a no shooting zone, then you have a safe spot. But once you incorporate the battery issue you can either make people bring enough batteries. If it's only a weekend long game then it really isn't going to be that hard, and make them find their own means to charging (Car chargers/generators) or you include generators, and the gas to run them. With this being said as well you'll also need to remember to have fire extinguishers. Most people run LiPo batteries nowadays, and there's the popular saying with those 'it's not if they'll blow up, but when' Having a 2 or 3 cell lipo blow up in a forest is very bad stuff, and if we have generators, gasoline, a handful of other lipos and there's probably gonna be more flammable shit like propane. You have a recipe for disaster.
I know it's the whole Safety Sam speech that nobody wants to hear. But I would hate for people to overlook these things.