The first image of the final rendering reminds me a little bit of Observer game, it's nice. You said that you used decals right ? Did you use the decal tool that is inside UE ( if you rendered it in UE ) ?
update my POGress:wall, lamp, wires, air ducts. Quick texturing, a few decals(took from Scifi Kitbash Level Builder by Denys Rutkovsky, really inspiring work), some issues with lightmaps of air ducts
update, rebuild whole scene with assets im currently have, just for playing with lighting and details, looking ugly. I think it's too many decals, but i can't really find the happy middle or whatever, guess i should looking for more references. Maybe make some new floors for testing or even walls