1) Don't know why'd you buy a KWC anything.
2) CO2 mags leak very easily, so you need to maintain them consistently.
3) 1 CO2 cartridge per mag sound about right.
4) You can buy UZI mags anywhere, including asia, and the states. Better finding them used then paying full pop for each.
5) Get age verified, will save you in the future from dropping 2K on a random retailer.