I'll ditto the ST comment. The ST is a full on professional camera meant to be the little sibling of the RTS III. The RX is a nice camera, but the viewfinder isn't as bright. Looking through the ST is a treat.
I'll also ditto the "just get Zeiss" on the lens front. The Yashica ML lenses are pretty dang good too, so if you find one cheap... Not the same as Zeiss though so don't pay full pop for the Yashica lenses. The Planar 1.7 is basically the same as the 1.4. Don't feel the need to try to get a 1.4.
If you want a cheap second body, the 139Q is hard to beat for the price. It is small even with the winder on it. The winder also has a vertical release if you shoot a lot of verticals. If you can find a Yashica FR1 it will take the motor wind you already have for the RTS. I have a FR1 that is totally hammered and it still works. Skip the other Yashica bodies though. They are cheap.