Since you don't have experience watercooling
Link to Watercooling starter guide http://forums.extremeoverclocking.com/t355358.html
Link to specing cooling requirements:http://www.over-clock.com/ivb/index.php?showtopic=20277
Excellent review site for radiators/pumps/etchttp://skinneelabs.com/
Basically, the necessary size of your rads will be dependent on three things:
1) The temperature delta that you can live with (higher water temps can dump more heat into the atm per square inch surface area)
2) The fan speed (within reason)
3) The heat disappated within your system (are you going for 5.8GHz? Or something more reasonable?)
Given a modest overclock, and reasonable fan speeds only one radiator is necessary. The advantage of 2 loops is that you can run the GPU loop at a higher temp than the CPU loop. The other advantage, of course, is that you can dump alot more heat into the system for a short period of time (heat soak) as well as having a higher cooling surface area. Given that you want a low noise system, two radiators as you mentioned are the best option.
In many cases, the pump is a major source of noise, isolating it is necessary to have a quiet system (bungee cord or the like and insulation). The pumps are cooled by the water circulating inside them, so they can be buried to keep noise down.http://skinneelabs.com/2011-2012-radiat ... arison/3/#
Looking at this radiator comparison, you see that the Aqua Computer revolution has the lowest water temps at low flow rates and low fan rates. This is larger than even a PA120.3, but it has a low fin density and flow restriction, so it can operate with low flow fans and pumps. Since all this has to work together, research research research.