Thank you for clarification.
Level streaming is not very powerfull in very small maps (which we are currently creating for our project)
Maybe in our next project we will go Bigger 
One follow-up question: You said that engine hide meshes and stuff which are occluded (like by wall, etc.)
But what about , if they are out of camera Focus in TOP-DOWN View? (meshes and actors, that are not currently in our viewport, but are “just around corner”).
Will engine not draw them as well, so I don’t have to worry about Culling?