The image was 1600x1200, which is pretty much what my starting base is.
Yes, the start size. Granted, this is "a lot" of extra work, but perhaps some option to have curve for start size. If the base star size is 2px, perhaps a second layer with 1/6th(or so) as many stars at 3px, and perhaps a third layer with perhaps 1/20th of the stars at 5px. Granted, the numbers may be bogus as hell and it may not work like I am thinking it might, but hope you should get the point. This is not so much a big deal (though it would be way nice) as being able to start with bit larger stars from the get go.
I would say one script. Since you have the power of Python(GUI-wise) and you are really working on such similar stuff, I would say it makes far more sense to keep everything together. Ultimately, you would have to create(or have an existing) a starfield to populate your nebula anyway, so it might as well be in the same script.