Hi, I guess it might be a lot easier to generate it procedurally / by seed as the player moves around the map.
Just doing some quick calculation. Imagine you want 1000 “things” (e. g. any actor or any instance like tree, rock,…) per square kilometer which will be a very sparse environment. 32 bit times nine (three times for the location, three for rotation and three for scale) that times 1000 and then times 40.960.000 will result in about 1.4 terrabyte of data. So I guess that would rule out to use it as game since then people would need to download and have that amount of data on disk =)
That then means you need to use the landscape grass type to place all your trees rocks,…
So with 10 “things” per square kilometer you would end up with about 14 gigabytes of data which might be ok. Of course it might/will be boring for any player to have only 10 “things” per square kilometer in the world…
Also the landscape is stored as 16 bit texture with one pixel per square meter and all the landscape grass types use a texture of the same size (no idea whether those are 16 bit though). So no idea of UE uses any compression on the landscape texture, if not then you will end up with about 82 gigabyte for the landscape (not counting any grass layer) which again will/might not be feasible for disk usage.
In the end there is no reason you need a world of 6400 km by 6400 km. You only need to have that the player has the illusion/thinks the world is of this size.