Beginner questions: scale and modularity

While i’m still learning the basics of UE4, i am really confused about some concepts and it get’s worse the more i read about it online.

I have set Blender to UE4 units, like WorldofLeveldesign said in his YouTube-Video and it matches up just fine, but he also said, if it doesn’t “feel” right, you may have to rework your level. I have built a basic map in the fps-template and it definitely doesn’t feel right.
So, what good are units like 2m or 4m if they don’t match our real world perception and i am supposed to “eyeball” everything anyway? When building meshes, am i supposed to keep in mind, that 2m are actually 3m? I wonder, how people make the scale in those architectural visualizations seen on YouTube which “feel” right. Is it all a matter of camera settings?

For level design, everyone says “always go for modularity” but, for example, using modular wall pieces causes terrible lighting issues (even the starter content architecture meshes have these problems), so some people say you better make whole wall pieces. If i need a 6m wall instead of 4m, do i really have to go back to my modeling program and make a new asset for that, ending up with dozens of unique parts? Is it still okay, to make some rooms with a more unique size as a complete model and keep the rest modular?

Scale: I would always use real world scale as rule of thumb. Unreal uses the metric system so as long as your modeling program is set to that, and your export setting are also set to export in metric, you should be good to go. As for the “feeling,” this can be a tricky one. If you are making a first person game, the camera settings can get you 95% of the way there if you’re scale is correct. Try playing with the FOV and making sure the height is correct to get that closer. I’ve never had to tweak sizes of meshes compared to real world to get it to feel better, it’s always been a matter of camera.

Modularity: Do what works best for your project. If you are creating architectural scenes, modularity isn’t important. You can create everything unique as long as it isn’t a whole city. If you are making a large game, it can be more important to make sure you aren’t using too much memory.