Somewhere, there is a little tute on how to create a background starfield in Photoshop using the grain filter I think.

However, why not try a variety of small, different size, spheres, adding glow?----and surface replicate them to a deep blue? plane which, rendered, becomes you background image?

If some of the  replicated items were lights, you coud give them vary-cross, star light effects also.

Brian

bwtr