Never having been to Paris - much less central Europe proper - I unfortunately am not in a position to add any suggestions from past experience. I will say if it were me in your position I'd be looking to somehow blend quality accommodations with terrific scenery, onboard service amenities (a good dining car, not a walk through cafe) and an affordable price. High speed has never been a selling point for me.
That said, you've put together a really impressive itinerary here, MSY. I hope it all turns out to be a fantastic trip - for you both! ^^