As to attaching a P25 to an RZ I or II, you can use a "dead plate" like the ones from Leaf. Ther eis no electrical connection between back and body. I believe you need to trigger thePhase back with a "one shot" cable that provides the wakeup, and a lens to back cable. I thought this method of firing the back was too complicated, so I went with Leaf backs that do not require a wakeup.
I believe that the Hass. V to RZ adapter provides a wakeup signal, but I may be wrong. I also believe that th adapter does not rotate. The Leaf adapters rotate.
Good luck. I think an RZ Pro I, a few lenses, and a few finders, at under $500, is one of the best MFDB platforms you can get. Soft mirror return, GREAT lenses, tough, leaf shutters.