I would probably do it like that, but then again my computer is very fast, so it wouldnt take very long to compile.try making the ships and things first, then putting in the background so you can narrow it down.
You must not have selected the shader then. In the editor, you will see the sky shader will "sky" text tiled on your walls. Also, make sure the outside of the box is textured with "caulk" in the systems textures because you don't need your map to draw unnecessary shaders.
I think your thinking of ideas too big and complicated for you. From what you've said I gather that your only an ametur. So just think of small ideas and easy maps like dueling arenas, there probebly the simplest. Single player is the hardest. And you need to use BSP fullVIS if your using Jk2 Radient and if your using Gtk Radiant (any version) use BSPfullVIS -meta