I am using an F4 200mm Newt and an ASI1600mono - can somebody tell me either how to calculate, or ideally just what catalogs I need to download for the blind plate solving?
If I calculated right your FOV is 1.27x0.98 degrees. The index downloader suggests the narrowest index be about 20% of your narrowest FOV. So that would be 12 arcmin = Index 4205.
Unless you are pressed for disk space I would recommend downloading Indexes 4203-4212.