yeah as said by a few... G&P's are workhorses .. they are expensive but once you figure the upper and lower reciever set sell for $250-350 ALONE (in canada) it isn't too far fetched..
the internal issues with G&P that many have come across seems to be hit and miss.. I have a friend/customer that bought 2 of the same G&P m4's (custom imported stock, not cnd market modded) and they have both seen 20+ thousand rounds each (no joke .. infact that's probably a bit of a low guess) with no internal issues at all ... he's a box mag user that's slowly comming around to midcap use.. so thats all long hard firing
as for the amount of mags to carry... that will really depend on you, your play style, and your trigger finger
personally when I'm not on my saw I carry 10 50rnd mags .. and I can't remember ever running out in the middle of a game. plus side too, unless your looking for a specific type/brand etc M4 mag... they are cheap.. and everywhere... I have a drop pouch on my rig.. but 95% of the time I forget it's there, in the middle of a fire fight I drop my mags to the ground and keep going... haven't lost any yet!
for the pistol... I'm a TM fanboy .. however KSC/KWA series is right up there with TM's .. for me personally my pistol isn't a backup it's another option on my person... I run TM desert eagle(s) and never at any point is there ever a shadow of a doubt in my mind that if I have to sling/drop my primary for what ever reason that I can't stay in and go toe to toe with aegs on the field with it(them) .. so full metal, etc etc etc isn't a primary thing in my brain
for alot of other people the pistol is a backup/secondary/last ditch/holster accesory .. full metal, full proper trades, etc is important to them
take my opinions with a grain of salt.. I'm not a 'normal' player .. nor am I elite.. etc etc.. ofcourse I want the best on the field .. but in reality .. if it works game on
welcome to airsoft and definately check out your local scene from what I understand theres a really good airsoft backing/group(s) in your area for you to feed from info and experience