before i start nit picking, i'd like to say it's a nice clean build
BUT;p it seems to me the machine may be a tad on the loud side? you got a whole lot of exhaust and not enough intake and intake sources are not filtered so you'll have a dust problem after awhile. the corsair intake fan is a excellent idea, however you do lose the ability to mount your N520. I'm also not sure how well the corsair fan plays with the rest of the case in terms of clearance with the drive cages / vid cards. however if you can make that work it'd be a nice addition to the overall cooling solution. personally, I may have gone with a silverstone SST-AP181 instead of the corsair for more stable case mounting since the corsair is a tad large for that case. another thing to keep in mind is filtering the intake air. it's harder to accomplish in the way you have mounted the corsair, but possible with a few rubber washers on the fan mount. (a pain to clean tho
) other concerns are the dust buildup around the intake fan area. there will be a patch of dust just outside of the corsair fan that you have to wipe down maybe once or twice a month.
as for the CPU cooling, i'd go with either the H80, or maybe a Thermalright AXP-140 for a quieter build. the AXP-140 would be in a good position to take advantage of the cooling air from the corsair fan and you may be able to run it fanless.
one big caveat I'd keep in mind is where you put the machine. if you put it in a semi enclosed location, the corsair may recirculate the warm exhausting air from the back of the machine and pump it back into the box.