Humi that gain should be multiplied not divided but the ADU levels seem right.
Mark if you want to go super in depth then this paper by Richard Crisp whilst perhaps a bit overtechnical has some nice summarisations and principles in it:
http://www.narrowbandimaging.com/inc...3_expanded.pdf
Page 103 actually says the suggested ADU level (ADU= analogue to digital units = number of electrons).
Also the number of flats for 8300 sensor is 5-8 in an earlier page.
Another interesting point in the paper is if your RAW images are brighter then you need brighter flats.
Greg.