None of the powershot cameras have a mechanical reflex mirror - they are not SLRs.
Supplemental lenses are not the best optics, but any model with a bayonet probably has a wide angle and telephoto attachment that can be added.
The larger the sensor, the better performance in low light, in general, although noise suppression software plays a role as well.
External power is not usually a problem.
Personally, I think you should look into the A6xx series for several reasons
they use high capacity memory
you are not buying a dead battery and having to source a proprietary charger
for eventual 2K or less resolution, you don't need a 12 megapixel sensor
having multiple cameras might be better than putting all you eggs in one basket, so to speak
After a certain point, I hear that the later cameras didn't have a "Real" iris.... not sure about that but it may be something to look into.
hope this helps
