Sorry, I didn't read the 5th and 6th question when I PM'd you Fatarion.
It is very possible to create stars, planets, and galaxies with textures. Galaxies, I think are the easiest, because you can just google and image or as you asked, go to
Hubblesite or similar places and download a picture of the galaxy. Face on galaxies are the best, because those are the ones that it will work with. Simply go to your Media folder (C:\Program Files\Universe Sandbox\Media), and find the pictures called "Galaxy-X", and replace it with the new one you had. Make sure the file names are exactly the same, and you rename the original and keep it.
Textures for planets are also easy, but the way I know to do it requires a modification of the XML file, which isn't that difficult. If you'd like to do it I'd be happy to explain.