As for the texture compression format, the safest bet is what Bethesda used. For my own project, though, I've been using BC7 (d/n/s) for weapons/clothing, and vanilla formats for environment/props, as I feel that BC7 pops out more against the vanilla formats, which are noisier to my eyes. In any case, you may want to maximize your texel density of your textures, so that if you had to lower the resolutions for consoles in the end, they will survive the conversion. Bethesda used a lot of UV mirroring/overlapping to maximize texel density, and their assets are a great source of learning in this regard. Reducing the number of material files loaded by combining multiple elements can be a good idea if possible (each material files will add draw calls in game).