if your budget only extends to 1500 dollars.... wait for a month or two and get a qhy for a few hunge more. the smaller chips are just too small to do much with (eg you will be lucky to get a A4 print).
Thats my advice but at the end of the day do what you want
Pixel sizes are given, you don't need to calculate it.
Arc seconds per pixel get a free program from New astronomy press "Ron Wodaski's CCD calc"
What you want to do in a perfect world is get 1 arc sec per pixel.