I do downloaded my texture from Megascans which is available both on Epic Market Place and also they have their own web site and MegaScans are part of Unreal and free to use content with Unreal Content.
They also have meshes which has multiple LODs which determines low poly and high poly depending how close camera is); They also have a small Quixel Bridge App that imports from 3D softwares (Blender, May and others) and download or Export to Unreal…
EDIT: MegaScans Plugin works with UE4.25.3 release so below note is only for UE4.25.2
Note !!!!!! : They have a plugin to export directly project that adds a button on your Editor . It installs and brings the materials and models into your project but if you install Unreal Editor gives error when compiling C++. The build file needs to be modified to include a module rule. I could not figure out. I deleted it after i installed ) So be aware !!!!!!!!
I also followed a tutorial to use Normal maps just to have basing understading of it and create some multiply functions, scalar parameters to setup a base stone_wall_material and created an instance;