I wonder if the server would be overally taxed if you have too many players all being tracked and each spawning in objects/missions.

I have a similar zoned arangement in a script development. However to stop multi spawning I have a randomised selector including null missions so that there is chances nothing happens aswell. Once activated though the zone is on timer (randomised period), so that following player does not activate again repeatedly.

As much as we want a open free play, the designer of the missions and pack should consider operations that target players attention to an area. Otherwise you might as well play single player. With that, the zones could be confined to a battle area of importance and thus lower specific mission per zone trigger and importantly the need to have a gazillion missions which do nothing.

To add more life, I populate the places players will see most and the rest I just leave quite bear. I think its a balance between performance and looking good. I will liven up airfields and targets usually. Maybe the docks. A few barrage balloons. Trains can have a good livening effect as they travel far and are really visable.

But for things like an AAA battery in a wood, just plonk them down ;)
No one will ever see them.

I would have to agree on most of that. Even road traffic is difficult to detect unless you know it's there. With the Regent Bus being a possible exception of course.

I did write the LiveMap class to support a specified limited region on startup and ignore anything outside so its very easy to have it live up a focues part of the map.