Have you played with the loading range in World Settings, all the actors with Is Spatially Loaded depend on this setting.
I have a map with ~7000 actors, it was well over 100k but moved everything apart and got it down to the 80k’s.
8 - I don’t think we have that functionality, UEFN Blocking refers to blocking an actor from going somewhere, It would be nice to have something like a loading volume that doesn’t load contained actors until it’s entered or something.