Great info, thanks!

The “best” length of subs depends on a whole range of factors – brightness of the sky, focal ratio of the optic, quality of mount/guiding, etc., full-well capacity of the camera and more. Once a sub is long enough that the image is limited by sky quality rather than electronic noise, there is no advantage to exposing longer. More subs also give better results from stacking, since sigma clipping methods can be used. In other words, it is always a compromise. Try a few different times and see what you get. For myself, when shooting at f/6.8 I shoot 15m in RGB and 20-30m narrowband. At f/3.6, I’ve had great results with 2m subs. As for guiding, the need for this depends on mount quality, focal length, accuracy of polar alignment and exposure time. With my dslr at focal lengths from 24mm-100mm I do not guide, but I keep my exposures to 3m or less. Light pollution filters won’t do anything to help with moonlight, since the moon emits light across the visible spectrum. LP filters remove specific wavelengths. They have pluses and minuses too — particularly affecting colour balance. The upshot is that exposure should be long enough that the noise in the shot is limited by sky quality rather than camera noise. Longer than that doesn’t really add anything, and reduces the total number of frames for stacking. See https://starizona.com/acb/ccd/calc_ideal.aspx for more information. You’ll probably need longer exposures to get a sky-limited result if you are using a filter. Good luck!