NB = narrowband (the Ha and Oiii filters) and BB = broadband (the RGB filters). Because I’ve got a lot of light pollution I use a lower gain for the broadband filters since they let a lot more light through.

I only count exposures post-rejection. The morning after imaging I’ll look through the pics and delete them if it was cloudy, out of focus, not centered, or if the stars trailed. The rest go on to get calibrated and stacked for the final image.