Choice of Z-probe on the RailCore is one with no single right answer, as with any 3d printer. There are always tradeoffs. The most important factor is repeatability, you want to choose a probe that will give you consistent results at a given location.
A Bltouch can be using using the BLTouch in the main Thingiverse page. You'll need to space the height out to match your particular hotend. For a V6 having a pair of the brass threaded inserts between the mount and BLTouch is near perfect. See the picture. I also used a bit of belt to dampen vibrations since mine was somewhat noisy.
To connect to the duet you need to use 2 wires off the Z-Probe port, and 3 off of the duex5's PWM1 port.
The full BLTouch Duet guide is here: https://duet3d.dozuki.com/Wiki/Connecting_a_Z_probe
The settings I use for my BLTouch in my config.g are (Comment out the IR Probe lines, adjust the Z trigger height as needed):
M558 P9 H5 R1 F50 T6000 A5 S0.02 B1 G31 X2 Y42 Z2.68 P25
You also need to make sure the deployprobeg.g and retractprobe.g are in your /sys folder