Some technical questions on realistic scene

Hello, I am totally new to Unreal and I wanted to understand how to actually model for make use of the best rendering possibilities in the game , I have checked some tutorials and they talk about lightmaps, but in order to make use of those I have not understand how.

Many of my models use shared textures and tiled textures, with uvs that sometimes go beyond berders or overlap as the same texture is reused, so I quess those models need to be redone in uvs? Or the game engine makes new uvs for the lightmap and store for the model? Iam confused, I have seem people import super high res models like from Archiviz and they seem to work fine without even having an uvmap ?

I am not understanding this process, could someone point me where to go or what to read?

thanks a lot.