Large procedural outdoor scenes without preprocessing?

I am interested to create large outdoor scenes with procedural buildings on the fly. Now my question, is this possible in unreal engine?

I read that it generates voxel volumes for voxel cone tracing first, so in case of procedural geometry that means it cannot be generated on the fly and only in advance?

Next, if generated in advance, would it not be a major memory consumption for the voxel data in case of many skyscrapers with interior?

Further, are the other things required to be generated offline first like lightmaps or collision volumes for physx?

Last question, can a building be broken into smaller parts for having level of detail not for the entire building?

Looking forward to the answers.