With the P2 you need to get a separate bracket for the GoPro
This can be a simple piece of plastic that attaches it to the bottom of the P2, or you can buy and fit a 2 Axis or even a 3 Axis gimbal - which stabilizes the camera and can tilt (2 axis), or tilt and turn (3 axis) (though only a 2 Axis would be controllable with the stock Transmitter)
The ZenMuse is the matching gimbal sold by DJI, however its $$$ and there are loads of other much cheaper (probably lower quality) gimbals available that can be made to fit the P2
The Vision has a video downlink (aka First Person View. FPV ) , which the P2 doesn't. If you want this, you need to buy a separate video link transmitter and a receiver / screen unit, (or FatShark googles etc).
I'm not sure if the Vision as OSD (On screen display of speed and height etc), if you want this as well, you need an OSD module to put between the video out from our GoPro and the video in to your video transmitter
If you want full details, please post again, and I think people can give you specific info on gimbals and OSD and FPV etc etc