I wrote an article that has just been published in Petapixel. In the article, I offer some insight on megapixels and camera scanning, particularly for 35mm film originals.
We are hitting a point of diminishing returns on pixel density where going to very high resolution sensors like the Sony A7 RIV (61 megapixels) may actually get you inferior quality to lower resolution (30-45 MP).
If you are putting a camera scanning system together, you should carefully evaluate critical sharpness and make sure that you can get consistent sharpness across the entire frame.
What I did not say specifically in the article is that use of a rail-based system becomes even more important as you go to higher megapixels since it allows easier alignment of the camera to the film I stayed away from any specific hardware mentions in the article.
If you are interested in rails, which offer precise alignment of the camera and film, I’ve just produced a new batch of the PS-4 version, which seems to sell out as fast as I can make them.