If the chair rail is glazed on both the top and bottom edges, it shouldn't be a problem. Line them up next to each other, just as they would go on the wall, and you'll be able to tell how it looks. Sorry, I don't understand the problem with your second question. I can't see how the chair rail affects the crown molding. Perhaps a sketch would help.

As far as your second question, in my prior home we had tiled our shower to the ceiling and put in crown moulding in the room. My GC put crown all the way around including the shower. He used an extra piece of wood for the crown not over tile so the ultimately they were the same depth. I hope that makes sense.

Are you talking about the raw edge of the chair rail when you end it at the start of the full wall field tile in the shower? Can you miter a piece of rail to the end and then start your shower field tile next to the new rail finished edge? It would be a tiny mitered piece I would imagine but would finish it off wouldn't it?

You can either use the AO chair rail, or use a painted wooden one. Either would look just as good.

Many thanks to all! I will go with the AO chair rail since its running through the shower also and use the extra wood underneath the crown to solve for the depth differential!...
Unless of course I change my mind for the millionth time... maybe beadboard instead of tile...