Cv is a measure of the air flow rate.
It can be difficult to determine if the manufacturers specs use a similar but different measure.
NPT port diameter is an internal port inside the solenoid. You have to find this spelled out in the manufacturers specs too.
To set the pressure relief valve you put the system under pressure and turn the end until the air escapes at the proper psi.
We have some general information on pneumatic layouts and setup here:
http://www.team358.org/files/pneumatic/