Nex4000

Is possible to have carplay on the unit and play movies rear headrest screen?

Carplay doesnt support video.

Movies in the sd card.

If movies are on sdcard , the dual zone should work to play videos. as VBLUE42 stated Carplay doesn't support video(yet, who knows, Apple may open up some api's in the future). You would have to setup rear to sdcard. You cannot use usb1 for movies, since CarPlay uses usb1. 

I haven't checked with 1.08, but the previous version would not allow my nex 8000 to play a movie in the rear zone while car play was hooked up, I had to physically unplug my phone from the nex to play from SD Card or USB.

While you have the phone plugged in with the car play update, you can only play movies from a disk for the rear monitors,