How do I know when the system is at the correct pressure
The instructions which come on the gas container are not clear regarding the setting of the ambient temperature and determining the correct system pressure.
Having set the temperature is the correct pressure within the V created by the two red lines.
For instance: Temperature set at 65 deg would the correct pressure be between 25 and 35 PSI
That is correct, if the pressure is on the low side of the V (25) it would be best to add a little until the pressure increases.
If it is already around/above the middle pressure (30 to 35) the system is OK.