Hi Al
For the Moon, at the prime focus of the Mewlon 180 F12 (2160mm) or C9.25 F10 (2350mm) I think I have the gain set to around 300-400 but this can vary if say, a bright region like Aristarchus or Tycho is in the FOV.
I usually have Gamma set hard left (can’t remember the value!).
And yes, I try to keep the whites at around 220/240 as often, seeing can make this number shoot up to 255 for sporadic moments.
From memory, provided the seeing is good (6 to 7/10) I tend to find that stacking 200 to 500 frames does give me more flexibility with the final stacked image in terms of trying to get nice tonal transitions and sufficient sharpening to make the detail pop, if it there in the first place. In the past I have really struggled with stacks of less that 200.
On nights of seeing 5/10 or less, I tend to end up with quite soft images that really aren’t worth the space on my hard disc!
Sadly, I don’t have your background in stats so I am more driven by the variables of just eyeballing the final results on an uncalibrated monitor, leaving scope for a lot of subjectivity and variation!
Cheers
Dennis