I'm a relative newbie as well, so I probably can't answer some of your questions, but my most recent target was NGC7000 and my total exposure time was very similar to yours. I was using a guided star tracker and a wide field refractor (250mm), un-modded DSLR and I managed to get a decent image (for me anyway) with 3 hours and twenty minutes of data. I shot 100 subs at 2 minutes each so our data accumulation is almost identical. The biggest difference I see is your amount of light pollution you are having to deal with. I shot from a pretty dark sky (Bortle 2). Bortle 8 sounds pretty severe and will certainly affect your ability to frame and shoot your target.
I think ISO 1600 may be a bit high. Sure it's letting in more light, but with all the light pollution it sounds like you might be getting a lot of unwanted ambient light as well. Cameras are all different, so that will probably take some experimentation on your part to see what suits your camera. For mine, which is a Canon, the sweet spot seems to be about ISO 800.
Here is one of my single subs from a few weeks ago. 2 minutes each at ISO 800. Again, this is from Bortle 2 skies, but I could just make out the nebulosity in my test exposures that allowed me to frame it pretty well. If you have the ability to travel to darker skies that will certainly help.
Also, calibration frames are important! don't skip those.
Edited by RPitts62, 11 August 2022 - 11:53 AM.