I would suggest an Intellect 8.4V or 9.6V battery from GI or a similar place:
http://www.airsoftgi.com/product_info.php?cPath=27_47&products_id=3372I personally have this charger:
http://www.airsoftgi.com/product_info.php?cPath=27_74&products_id=3358It's hard to find, but well worth it.
For an AEG I would suggest a 6.03 mm diameter inner barrel. To be blunt, the more you pay for it, the more accuracy you get. Brands wise you have some choices: Madbull being low end, Prometheus being mid-range, and PDI being high-end. There's a few other brands out there, but I don't know them so I won't discuss them.
Like victor said, just go with a red dot. Cheaper is usually worth it. Magnification is usually unnecessary, but 2x can prove handy for 200+ ft shots.
Only bother with an RIS kit if you plan on mounting things that go on an RIS (IE flashlights, lasers, foregrips, etc).
You probably want an M120 spring (which shoots 0.2g BBs at about 400 FPS).