To answer the original post:
You can convert Windows S to a proper Windows very easily, see
here.
It has a 64GB eMMC which should just fit Windows and a few astro programs but it will probably be quite slow so I wouldn't plan on doing any planetary imaging directly to that drive. Perhaps you could get better speeds with a fast SD card in there but you'd have to test. For deep sky imaging I can't see why it wouldn't work fine.
It's certainly not an amazing computer by any stretch but it's pretty impressive what you can get for under $300!