Most IPSC people I see have 5 mags. I carry 8, but bring about 15 to a match to save time. The P7 I think is standard, I know for a fact it isnt production as I checked the list.
Also are you aware that some version have a bad tendency after a few rapid shots to get really hot and can burn your hand? This may or may not be an issue depending upon how fast you fire it. Plus I have seen holsters for it, but you will probably be limited to more high quality leather ones, Im not sure you could get a cheap kydex style one for it.