How many images do you composite together and how much post processing do you typically use?
It depends on the target. With planetary video, I use a few seconds of video, and the stacking program I use splits the video into individual frames. Deep space objects I might take 50-100 1 minute exposures for good detail.
If the objects change over time how do you know that doing this isnt giving a false impression of the object? Taking a video of a spinning wheel, for instance, and then mashing a bunch of frozen frames together, is going to give an innacurate representation of the object
The only time that would really be a concern is with small and close objects like planets, but even then they are so bright you only need a few seconds to a few minutes of video for a sufficient amount of light frames. Sure, Jupiter's moons might be slightly different from night to night, but there's no way you can see detailed change in its clouds in a few minutes time. As for DSOs, I'm pretty sure some of the nebulae we see today look almost exactly the same as they did a century ago (for amateur astronomers at least) because they are light years wide and many light years away. There's no way I would see a change even with several weeks worth of imaging sessions on some objects.
Missed the post processing part. First off, I'm bad at post-processing. Usually I just selectively alter the brightness/saturation of my target for a bit of extra detail in photoshop. I have recently picked up some scripts (is that the right term) for photoshop that round the stars near the edge of a photo due to the scopes optics as well.
Changing the images to look more appealing doesnt seem like youre giving a genuine representation. At what point does it become artistic interpretation?
By that definition, taking an picture of anything is an artistic interpretation. There are only a handfull of bayer patterns that exist and they are all merely approximations of colors our eyes can see. I see your point though, and the goal is to keep these changes as minimal as possible as attempting to gain extra detail in dust cloud patterns can easily go overboard. Whats really going to cook your noodle is when you realize that many astro images are composites of monochrome images with separate R/G/B filtered images combined by software.
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