Great results for an entry level CCD there Paul. I wouldn't worry too much about the stars on luminance data. RGB is where it counts. Indeed take short exposures, then layering them using the lighten blend mode to reduce their saturation. Another thing you can do is before you perform sharpening (of any form), drop the white point by ~50 counts. Sharpening typically brightens highlights so you are preventing clipping by dropping the white point before hand.
