Well each GTX680 has a TDP rating of just under 200 watts so ideally you would want 2 120's for each card and for the CPU you could get away with just one 120 rad. Given you running 4 way SLI only the first two cards are going to be running at anywhere near to there maximum TDP the 3rd and 4th given the normal complications of multiple video card scaling will be at around 30% to 40% so there's a bit of let up.
If you want to watercool properly and want a quiet system with overclocking then your going to need a case that can support at least
two of these , there are other options I know a lot of good ol boys around here are fans of the Hardware Labs Black ICE rad' as there slimmer and are better for clearance the draw back is the FPI is higher which means to get the performance from more FPi you need run your fans faster (at least that's the theory).
You don't have to get two 480's you could get a couple of 360 rads and and a single or dual rad in somewhere else but your aiming to get 7 to 8 120 rads in a case for that sort of hardware.