Biased opinion here, but I'd go the RP60 route everyday and twice on Sunday. The Pana controllers give you access to ALL camera functions, most importantly letting you adjust camera shading/iris/color control. I've not used the xkeys joystick, but other generic joysticks connected to my Panasonics (AW-HE 40/60/130) thru vMix results in sloppy/sluggish motion control. The Pana controllers let you assign different speeds and scope of functions to preset positions stored in its controller, something you will never get with aftermarket controllers. The control from my RP50 joysticks is VERY precise and I do follow movements frequently on this controller. Also, I prefer to have another person besides the vMix OP controlling camera movement, so having a controller not tied to vMix makes a lot of sense to me.

To your other questions...

1. Yes one network cable to the cameras gives you POE power, camera control, and NDI video. If you assign the camera IP to the vMix input you can have rudimentary control of camera motion, but I find recalling positioning this way rather clunky and the moves are not "on-air" worthy. Handy when my camera operator is on break tho...

2. the Pana controllers simply connect to the same network your cameras are on and talk directly to the cameras, so no you don't connect the controller to vMix.

3. No data