Should I use World Partition/Composition for median-sized world?

In ue5 you can make your own Data Layer based system for that.

Personally, i would still do it manually.

And also, there is nothing wrong with deleting and creating actors from within another (manager) actor.

If or rather when the load gets to be too much, then you break into C++ and make yourself an Async system class to replace the actor class of the manager with (theres examples on how too by now).