You don't need that much for this task. ANX already has everything you need I think.
As a starting point for the GUI you have a couple of (XNA) options: starLiGHT.GUI, Nuclex, neoforce controls are good starting points. They don't run out of the box (I will change that soon for starLiGHT.GUI) with ANX but it should not be that much work
to change the namespaces and tweak some things.
The bigger part is the RenderSystem, InputSystem and maybe the PlatformSystem. All of them needs working drivers. If you are able to run OpenTK (or maybe SharpGL) on cosmos this will be very easy. The default RenderSystem (and in case of OpenTK the InputSystem)
should work out of the box. If not you have to call the drivers somehow.
BTW: This is a great idea. I saw Cosmos a couple of month ago and I think it is a very promising and interesting project. If I can assist you to get ANX run on Cosmos let met know.