What kind of chest rig/plate carrier you get depends on your play style.
If you want a "High-speed Low-drag" setup, I'd get a battle belt or perhaps a mesh vest. The downside to a battle belt is that you can't carry that much ammo, but with a high-speed loadout then you don't really need as much ammo because ideally you would move more than you shoot.
For a tank sort of play style, a big plate carrier with lots of MOLLE room would be ideal because then you can carry lots of ammo and such. However it weighs you down a bit, which to some is a con and to some is a pro.
For something in-between, a larger chest rig/lighter weight plate carrier would do you good.
Personally, I have a Condor chest rig (I think it might be a discontinued model, I got it used and haven't seen it in any airsoft stores) and I can easily fit plenty of ammo with my pistol rig on my drop leg. I'd like to run a battle belt + H-harness as well so I can have the weight more evenly distributed, but I have yet to actually get one.
As far as your G36 mags fitting in the M4 mag pouches, I'd be surprised if they fit. I know AK mag pouches fit G36 mags just fine, but I've never seen them fit in M4 mag pouches. Which is why I suggest getting a "clean slate" sort of rig with just MOLLE on it, so that you can put AK mag pouches on it. There are also a couple chest rigs designed for AK mags that you might be able to find somewhere in the NW... One of them is NC Star which only holds 6 AK mags which would probably mean 3 G36 mags. The other is made by Pantac (It's a higher-end brand which is hard to find in a lot of places, but Airsoft GI has a ton of gear from them) which holds 12 AK mags, but it's not as cozy so you could probably fit 6 G36 mags into the pouches.
As far as MOLLE vs. fixed pouches, it all depends on how important modularity is to you. If you don't think you'll be getting more mags any time soon, then a vest/chest rig with fixed pouches would be fine. However, if you like to be able to move stuff around, then MOLLE is the way to go.
Here's some good options:
Condor OPS Chest Rig:
http://www.airsoftoutletnw.com/index.ph ... &Itemid=28Condor LBV Vest (chest rig):
http://www.airsoftoutletnw.com/index.ph ... &Itemid=28 (not sure about the pouches on this one, I'd bring a couple of your G36 mags with ya when you go to look at stuff to see if they fit or not)
Condor RRV:
http://www.airsoftoutletnw.com/index.ph ... &Itemid=28There are 100s of other options just on AONW, I only went a couple pages into the vests section.
I'm no gearwhore. I prefer "Connoisseur of Fine Tactical Garments".
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