Quick rule of thumb..
RNP APCH: TF to TF legs only
RNP AR: TF-RF-TF legs
GPS and GNSS are synonymous... GPS is the name of the US based sat system...globally, it is called GNSS. Currently only GPS (US), GLONASS (Russia) are operational...Beidou (China), Galileo (EU), and IRNSS (India) are a long way off, perhaps by 2020.
Interestingly, in the GPS accuracy diagrams, I never paid attention to the outer band at 2200m accuracy, Omega. It wasnt until I visited the Omega Tower, at about 1400feet,the tallest structure in the Southern Hemisphere, in AUS, did that click....