Optimizing Texture

Guys i have question . im creating an open world game and there are a lot of textures , more than 400 or 500 and about half of them has normal map as well . what are your suggestion for optimizing ? currently I want to create a 4K texture and put 4 *1K textures and unwrap the models in the way that they only pick that 1K texture . how much this is help full ? is this a good way ?