World Composition out of "safe edit area"

I plan to do a galaxy that don’t need to warp between levels, my idea is to ignore the “safe edit area”
Just found old topics in 2014 that tells me about “wierd calculating of physics etc” but only in combination with an open world landscape.
What about planets? Which each of them have their own physics?
For example:

Red are sublevels, black main level and yellow is the safe area