OK, I have initial results of my testing of the calibration frames.
In answer to your question about finding the average ADU of an image, you only have to open up the Statistics Process in PixInsight (Process | Image | Statistics).
I was worried about using the ASCOM driver generated Dark Frame you took. This is not usually recommended. Any time you calibrate Light Frames, you must exactly match Exposure, Gain, Offset, Temperature, Device Driver, and Capture software for all frames. Any mismatch can and often does cause problems. That is the case here. The ASCOM driver Dark frame, while looking to have about the right median ADU, did not work well at all. It led to massive clipping during calibration.
To get around the bad Dark Frame issue without the use of the ASCOM Dark Frame, I cheated. I took the Bias Frame and simply added 4 ADU to it to simulate a Dark frame. When the Light Frame was calibrated with the Bias_Plus_4 frame and also calibrated with a Master Flat made from subtracting the Bias from the Flat, the result looked pretty good but still suffered from clipping where too many pixels were turned to pure black (0 ADU). This was then fixed by doing the calibration again but adding a 900 ADU output Pedestal to the calibrated result. At this point, the Light was well calibrated and only had 2 pixels remaining that were clipped to black. (I strongly feel these would have been cured by using Cosmetic Correction which I did not run.)
After doing the manual calibration, the weak blue channel showed up again. I traced this back to the Flat Frame. A portion of the weak blue channel seen before may be coming from the color balance settings in the driver but another portion seems to be coming from the light source being slightly deficient in blue light. At least there was not the massive clipping in the blue channel seen before.
With more playing, I think I could come up with a manual process for you to follow to recover the data you have but it would not help you with your learning of PixInsight. The main thing to do is to try to find out what happened to your first set of Dark frames and then secondarily investigate the relative color balance of your Flat light source. (You can do that by taking flats with various light sources, deBayering them and examining the RGB Flat to see how the three color channels relate to one another. You want each to be roughly centered in the histogram although they do not need to be perfectly aligned. Just ensure that no color channel is too close to the left or right edge of the histogram and that the "free space" on the left and right is about equal. (In other words, get the average ADU into the 30,000 to 34,000 ADU range.)