Matthew,
The correct pressure readings are difficult if not impossible to give you because there are so many variables that will influence the pressure readings like location of charging ports, ambient temperature, and heat load from the evaporator core. Without knowing all of these, I can not give you the correct pressures.
If you want to add refrigerant to your dash air system, just add one can (12 ounces) and see how it cools. If it cools fair but not great after one 12 ounce can, add another, but if you need more than two cans the system probably needs a professional to look at it.
Gerald