I've been shooting a PM5 for the most part of this year, and I can honestly say theres very few guns I'd rather be shooting, in fact, theres not really anything except for a PM6 or DM6 that I'd prefer.
Theyre not as air hungry as a lot of people believe, provided you fill up between games, which you should always do anyway, you shouldnt encounter any problems. Having said that, a 4500 psi air system would definately be better, but a 3000psi will certainly do the job.
Upgrade wise, get a proto or dye on/off asa and an upgraded feedneck, either CCM or DMC is what I would recommend. I use ultralite barrels on mine as well, and it works like a dream, though the stock barrel is also very effective
I cant recommend a PM5 enough to you mate