Nope, for a gaming rig the most he will use is probably 6gb. If he uses more just go and grab another set of the same stuff.
More is pointless unless you use it. Ram is great for making a system fast, until your not using it. Then it just sits there.
Yes it' cheap but it's an extra 50 -70 bucks that he may not need to spend.
You're missing some key info for people to appropriately give advice. If you list your budget, any brand loyalty you have and the country you're purchasing from, you'll get much more accurate information.
I can't see why not. BF3 it will max for sure. Crysis 3 not sure. Its demanding on even the best possible systems out there.
A 680 on a 2500k gets 34fps with MSAA at 8x on V. high. Thats on par with what you'd get with Crysis 3. Reducing the settings a tad will get you a solid 60fps. Short of adding a 2nd 680 thats probably the best you can do. Going to a 3770k over the 3570k won't make much a of a difference there.