Workflow questions for building large city with level streaming

I want to create a large city with level streaming but I have some concerns about my workflow.

The way I thought I would go about this is to create modular pieces for buildings within my modeling program and then use those to construct full buildings still within the modeling program and then export the whole building to unreal.
I figure this would be better for performance since each building is going to made out of a few parts and multiple materials rather than hundreds of modular pieces each with multiple materials. That seems like it would be a lot of unnecessary drawcalls. This also lets me control how I want the building to look from far away when it switches LODs. I’m not sure how I would handle LODs if the building was made up of hundreds of parts.

The interiors would be their own separate mesh so that it can be loaded and unloaded if the player is outside of the building. The different floors or rooms could be loaded using volumes but I’m not sure how I would stream the exterior. Would all the exteriors be in their own level or all in 1. Would ue4 cull these when they are not in view?

If you guys have any tips, recommendations, concerns, ideas, anything at all I want to hear it. Does this sound like a good way to approach this kind of project?
Any advice you guys can provide would be appreciated!

Each building will have 3 LOds 1 will be complex with window intrusions, 2 will have no intrusions, 3 will be a box with window textures & cement such that the entire building is one texture ( which may be atlased with all the other biuldings on your block.
no point adding the window moldings to the complex building at export as every diff material is a draw call anyway. Better to export all the metal or wood facade bits as a mesh which can be in their own detail sublevel and hidden/dumped as you turn the corner of a block.

Good luck

You should test out with lots of examples if you’re planned workflow works really out before going into detailed production.
Regarding the interiors I would suggest to put them into sub-levels that can be streamed in if the player approaches or enters a building.