[otherguy]

For the PD wiring:

Although the photosensor isn't specifically called out I believe it would fall under <R39> (F) and require a 20AMP breaker.

<R40> defines wire sizes based on breaker sizes.
20AMP --> 18AWG minimum

I don't know the answer to your 2nd question. I'm not aware of any rules requiring a specific wire color to be used for the signal on the PWM lines.