This will guide you on the two variables you need to consider.
The pixel plate scale and the overall field of view.
The choice of plate scale is heavily influenced by your seeing conditions. If you had excellent seeing at say 1 arc sec, then a plate scale of around 0.4 arc sec/ pixel will gather as much detail as available.
The FOV should be large enough to cover the more interesting objects you want to image.
It's a compromise........
"Astronomical Spectroscopy for Amateurs"
"Imaging Sunlight - using a digital Spectroheliograph"
With current CMOS based cameras it's easier to photograph DS objects on high resolutions by lucky imaging - instead of few long exposed frames you take a lot of very short frames and stack that (rejecting bad ones too). This avoids seeing image distortion as well as tracking error. Bigger than usual aperture is also very much welcomed for this too.