Mapping Method Advices needed

Well you would not make it all in Blender and export it as a OBFF but rather use Blender to harvest working assets to create a source chain between whatever host application you make use of that you would export from using export by selection.

If anything the problems you think you might have is solved by pulling out a tree from the forest rather than thinking you have to deal with the entire forest in one big chunk.

Example.
https://youtube.com/watch?v=V1SsETZrSLA
Still a work in progress but 100% staged in 3ds Max, using edit in place, and then each building exported by selection, using the name of the object for identification and then exported by selection to create a source chain between 3ds Max and UE4.

Nothing new about this kind of work flow and has been around for years and the difference now with the Unreal engine is it’s a lot more compatible with already available pipeline features that makes it easier for a lot more people to work on a single project with out everyone tripping over each other.

For example.

http://3dmax-tutorials.com/XRef_Scenes.html

If you understand the logic it’s the same thing if you substitute 3ds Max with UE4 as the target using 3ds Max as the host.

As to how AAA developers makes their environments good luck with that, NDA’s and all that stuff, but when it comes to making environments in UE4 individuals with more general 3d skills have the advantage as the duck here is not really doing anything new but rather conforming to the logic of cloud based computing.

If anything UE4 requires a rethink of how things “could” be done as in most cases one can defer what they think is going to be a problem to when it actually does become a problem.