I loved this image, saw it a week or two ago and was really impressed.
I'm going to leave this thread here as discussion but please do *repost* the tutorial alone (as a new post) in the Tutorials section. That way it will be the first post and people can follow it easily, instead of having to browse through extended discussion.
Also note that "Through Camera" projection is not strictly necessary - it will give you likely more detail and if you are using a starfield image that shows exactly what you want to see in the background of your image, then this is the way to do it. But you can also use a larger spherically projected starfield image of the whole sky and set the Image Map shader to Spherical Projection. That way you get more realistic star coverage and you'll have unique stars wherever you look, instead of the same static star image.
- Oshyan