[Aavso-photometry] Beginner CCD Questions..

[Derek C Breit]

Can some one answer a question or two..
 
I will be using a 12" LX200 in alt az mode, and an ST7 ABG camera..
 
Any rough ideas of a general rule for my maximum useable exposure time, what
mag I can reach, what would be the minimum exposure time recommended to be
useful in regards to noise overwhelming the data, how do I concentrate on
areas of the sky with the least rotation from 38 degrees N Latitude?
 
Any ideas as to what magnitudes an ST7 can reach in 10,15,20,30,45, 60s .
or more?
 
I intend on doing NGC 7990 standards in V for starters.
 
I am very used to video when it comes to finding targets. My primary
question is what exposure time should I start out with to display mag 12
stars in an Auto Dark subtracted image, or a raw image,  with enough signal
to see the star above the noise, but not go too much deeper than that so as
to not be overwhelmed by field stars when I am still locating the target? 
 
Also, if anyone would like suggest any other targets to try (as a beginner)
feel free.. I already know I can put any star down to mag 12.5 on a CCD
Chip..
 
Anywhere in the Eastern sky is good..
 
TIA..
 
Derek