It does not fit directly. You must use the Godox S-R1 magnetic adapter to mount these accessories onto rectangular flash heads like the V860 series.
Yes, the magnetic rings allow you to stack modifiers, such as placing the honeycomb grid under the dome diffuser, for unique lighting effects.
Yes, but only if you are using the H200R Round Flash Head. It will not fit the standard rectangular or bare bulb heads without an adapter.