Pipe entry/exit

Base wall (holes for lights) and elevator track sections that tile together

Base tile, 1/8 tile talle, 1/4 tile wide, used to break up layers between tiles

Skirting Assets to create a modular border

Simple Pieces that Instance to create stairs

More Examples of modules working together

Start/end and repeat wire sections for use with cable tools in UE4

Elevator sections

Curved ceiling assets

Stair assets combined

Ceiling modules (at angle to show form better)

Floor Tiles (geometry to keep drop ridge between tiles)

More Skirting Assets

All Skirting Assets together

Replies
For the floor tile, i would do it only with the 'nDo/dDo' way (faster imo) but, great work here
One thing I want to point out is a lot of your edges look to be really sharp in your high poly, as your edges are looking sharp in the low. It's something I ran into with my last project, specifically using the double smooth workflow. I'd recommend chamfering some edges in your high poly to give you a better bake.
I've got a bit of a big update, I Used Substanace for most of the textures which work within a master material, These are taken from within the Unreal Engine 4 Project
(glass it a little strong on the refraction sorry)
Video Flythrough
https://www.youtube.com/watch?v=iMMPSr1gbAc