Single Huge Skysphere or Multiple Big Skyspheres for large landscapes with world composition setup as multiple levels? Is origin rebase needed?

I am not planning any network/multiplayer use just single player for this project but I need large landscapes.
I am trying to figure out what is the best way to setup quite large landscapes (32km x 32km or 66Km x 66Km) using world composition and each one would act as a different planet scene with a different skysphere look with its own suns/moons.
Is origin rebase needed with big landscapes without multiplayer or just using world composition is enough? I read that there can be issues with placing objects at a far distance from world origin but with any large landscape that surely can’t be avoided, no?
Ok, then I thought about having multiple very large skyspheres placed at a distance and each one with a large landscape inside it.
The first one in the persistent level would be quite small to act as a deep space scene. Then the others should each be a different level and act as a planet. The player would get back to the persistent level deep space scene after each mission in the levels/planets completed.
The problem is that the coordinates become really huge away from the origin, many millions uu/cm … is that going to cause some serious issues? Just by using origin rebasing for each landscape/level would solve any possible problem?

If such a setup would be wrong due to Unreal Engine limitations I was thinking about a different setup but still the player would be teleported far away from the origin due to very large landscapes being used. I thought about having to write more code to reconfigure/setup a single huge skysphere at runtime and just place the very large landscapes with world composition inside this single skysphere. Is that a better option? Having the landscapes setup as different levels still at a distance but all inside the same skysphere that would change when the player gets teleported on another level. It would be a matter of hiding the other levels from view for the player.

As an early test I tried placing two huge skyspheres at a distance with some objects inside but although it seemed to be working in the editor…if then such a setup would be wrong and blueprints and c++ code, physics of the engine would break due to being too far away from the origin I would only waste time placing landscapes and scenes like that if even origin rebasing wouldn’t make it work ?

So what would be the correct way to setup these large landscapes? Would both setups work ? Is origin rebasing needed in any case ? Should I spend more time coding the skysphere to make it change to simulate a different planet for each level at runtime and having all landscapes inside it or could I just place some very huge skyspheres at a distance with each one having a single large landscape inside?

I can’t afford wasting time doing the wrong thing so I need to know how to avoid Unreal Engine limitations that would make all the work unusable before doing it.

Simple concept schemes of the two setups. Question still is if these are feasible and if it is better to avoid having multiple skyspheres and just go for a single huge skysphere approach or not…

Single Skysphere:

Multiple Skyspheres:

Hey, have you found answers to your question? I would be interrested in knowing as I am going to meet sort of the same challenges.

From multiple tests using UE 4.15.x and UE 4.16.x I found out that the best approach is creating each level in its own folder so with its own world composition map pieces and its own skysphere… and so each would have its own persistent level…
Then use Game Instance to switch between persistent levels and save any data that needs to survive when switching.
So forget about setting up a huge skysphere with the maps inside or many skyspheres with their own maps… that speaks trouble with UE4 with its current limitations. Maybe UE5 will allow that setup to be made but for now it’s better to avoid any of that and use load/unload on maps and everything else. It requires more coding but it is the best way to use UE4 for managing very large worlds.
It could still be possible to define sublevels in each persistent level if needed although I don’t know if I will use those… that would depend on framerate drops, although I am targeting PCs with a good GPU for my first game I am developing.
From my tests distance streaming lowers the framerate in a quite unpredictable way. The best option performance wise would be to load the world composition tiles manually thru level blueprint code logic (or C++). The simple loading of tiles manually in the level blueprint with distance streaming disabled in a map with an untextured 8km x 8km world composition tiles based map showed a sustained 120fps in the editor while using distance streaming in the same conditions with or without LODs for the terrain had some huge framerate drops down to 70fps … which on any untextured map alone would then mean troubles performance wise when you put millions of poygons with thousands of objects and then the AI, any APEX/PhysX, effects of any kind, complex materials and so on…