That is a lot to think about. If i were you, i would look at what aspect will be viewed the most and use it. If you go with the 16:9 screen, you would have to mask the top and bottom, if you go with the 2.35 you would have to mask the sides for 16:9 or 4:3. As not every movie is in a 2:35.1 or 2:39.1 ratio.
If it was me, i would go with the 16:9 screen and constant image width. You can either mask or ignore the black bars on 2:35 content. I know a lot of people talk about zooming, and all, for me i like the content delivered in it's original aspect ratio, so black bars are not a problem with me.