It sounds like some of these questions might be more general Unreal Engine questions, rather than specific to the Cesium plugin, but I will answer as best as I can.
You can definitely create maps that aren’t set on earth, and as far as I know there is not a limit to the amount of maps you can have. Multiplayer is also possible but still has a few issues that need to be worked out - you can keep track of Cesium’s status with multiplayer here - Multiplayer Origin Rebasing Support Notes · Issue #480 · CesiumGS/cesium-unreal · GitHub
It is also possible to create VR apps with Cesium. You can find a tutorial here. Multiplayer in VR is less tested, but should also be possible. Having additional users in the session would almost certainly impact the performance of the app, but the amount of performance impact would depend on your engineering behind the scenes.
I hope this is helpful - let me know if you have further questions.
Hey, agallegos, I assume he’d like to know if he can use celsium’s chunk loading system to create his own maps.
In that case, there currently is no way to just take a section of the terrain and build a map from only that, or to edit the terrain. We’re looking in to some possible solutions for that but don’t currently have a timeline.