Recently the owner of a JG G36c myself, I've started to acquire some MAGPUL PMAG 30G (G36) mags. They feed flawlessly, look nice and are slimmer than the usual mags. Now, they aren't cheap (running around 30$ per mag) but it's a sure value.
As for the rig itself, I'd suggest looking around everywhere and buy what you prefer the most. I've seen people swear by chest rigs, and I personally can't stand them. In the end, you could run on the field with all your mags in your pants, but it would not be effective. Find what you're the most comfortable with and buy this. Also, I highly suggest buying a MOLLE vest/plate carrier/chest rig and the appropriate pouches. More expensive but if one day you want to change your setup it's all modular.