[Kos-Mos]

A few members here are using LiPo (including myself). They are good, but stay away if you don't know about them. (and you do since you asked).

They require a LOT more care and maintenance than regular batteries.
And a specific charger.

Other than that, your setup looks good.

+1 for the RDS. The ACOG will sit too high to be used efficiently.

Best bang-for-the-buck is a Tasco 30mm RDS. 50$ at Walmart/Canadian Tire. It is made for real guns, actually shotguns, so it is VERY rugged. Plus it looks perfect on a G36C.

An AimPoint replica, especially the Comp M2 version can be nice too. Make sure to get a straight or "L" mount. A high/cantilever will set it WAY too high.
And if you want magnification, you can add a 3x with a flip-to-side mount.

MAG brand magasines are way better than anything else. They are only 140/160 midcaps or 30 rnd realcaps. If you plan on playing small games with very little rules, go with the midcaps. They are more reliable than highcaps, cost about the same price for the same amount of BB and they don't make any noise when you run. Highcaps tend to stop feeding as soon as they are a little dirty or as they get older. They are good at start.

Stay away from King Arms magasines. They don't fit in my friend's G36C (way too tight, you have to bash the mag in and fight it out).

That battery is crap. And if it is the "nun-chuck"/"butterfly" type, it won't fit in your gun. You can get a special pack with 6 cells+2 separate cells with a short wire. These are 1700-2000mAh, but they require some modifications to the front section and you have to remove the switch.

Best bet is an Intellect 1600mAh mini. Made with 2/3A cells, they can deliver more current. That is what is important. 8.4v or 9.6v, as you wish. I would take 9.6v since the gun is pre-upgraded to 400ish fps. Might be hard on the 8.4v pack.