Nah, it only happens when two polys are perfectly on top of each other, it’s fine to put for meshes to be a bit sunk into other meshes. I guess z-fighting also happens with translucent stuff like hair too (unless using masked/hair shaders). But if it looks fine in that video it should look fine in game too. If you’re getting z-fighting it mostly means you messed up your 3d model in your modeling software.
One thing you need to keep in mind is that you would want to merge the meshes using Actor Merge at the end after placing the modular stuff or you’ll waste a lot of drawcalls.