When looking at the future you might want to think about the R4X (A or M) as a second body. When combined with the R3X provides you with a powerful system very capable of handing everything from 21 to 90 without external finders.
If you only every want (or can afford) a single camera, then I would recommend you take the Anchor Lens approach. Is there a focal length that you love (70 to 90% of your shots with) or a special lens that you are buying this camera for? Buy the body that gives you the features you want most for that lens, then go from there. In the Nikon RF world, the 50/1.4 Millennium lens would be such a lens for some. Easily one of the best 50mm lenses in the world. Is the 50mm your anchor focal length, then the R3X is it.
B2 (;->