The question your are asking is hard to answer, but I go ahead and at least point out some general things about the engine that I have noticed.
When your working with maps, you got to load a lot into memory by default…
Although unreal has the ability to load and unload things… overall its going to need to know a lot about what is going on…
But if you where crazy enough to build a very big map, like a mmo type world of a game where the map is massive… you certainly will need to utilize this ability.
Unreal has a good map splitting tool, but this would be a overkill for a basic game with player maps that where of avg size.
I dont know if unreal server mode is loading all the textures, etc but I bet this would be something that you could control somehow which would give you a lot of memory back if the textures are being loaded.
The Physics engine would need to know about most of the meshes, anything that is needed for gameplay will need to be on the server.
Blueprints are slow, so I would consider converting some of the heavy ones if they are shooting lots of raycast or creating spawned objects… etc in C
Just some ideas, not sure if any of it is useful or not… good luck either way!