I have found that there is no limit to the amount of sanding that can be done. After printing, I typically use an orbital sander running 80 grit to knock down the heavy lines. After that, I will bump up to 120 to by hand, then, 400. I also find that using a hand sanding block, and holding that steady while I move the part back and forth works better than holding the part still and moving the sand paper back and forth. After I have sanded and primed (and sanded) and painted, I will “sand” again with paper towel. It seems to take “a little something off“ before I put on a clear coat.
For my orbital sander, I use the cheapest one from Harbor Freight. It’s cheap, it works well, and it takes universal sanding discs that can be found at Wally-World. Unfortunately, the little attachment that is supposed to capture all of the sanding grit doesn’t help. The sanded material goes everywhere but inside.
NOTE: The clone trooper is a work in progress, and my hand sanding block is no longer made, so that link above is to something comparable.