No. With Make Baked Copy on, the original is only hidden (viewport and render) and a copy with the baked material is added to the OneClick Bake collection. Its original material is put back exactly as it was. The only thing added to it is a BakeUV map when it had no UVs or you chose Always Unwrap.

Yes. The maps are plain PNG files. The normal map is tangent space and uses Blender's bake swizzle, which is OpenGL style (+Y) by default. For DirectX style engines, flip the green channel or set the bake swizzle G to -Y before baking.

No. With Use GPU on it bakes on the GPU when one is enabled in Cycles preferences, otherwise it bakes on the CPU.