For those soon to go...
...if you trust 'the system' to automatically sort out your pension and gratuity because you've PVR'd, , you will receive a letter from the the AFPS a few weeks later 'reminding' you that you haven't sent them form AFPS1. This tells them how much (if any) you want to commute, confirms bank account details etc.
They will also tell you that you can do it online via JPA. Predictably enough, the link to the form is not 'AFPS1', but '(PENS1)'. The online version is pretty straighforward, although I did ring JPAC to explain one or two things.
Expecting another letter telling me I havn't done something else, shortly.