1) WD Greens are designed to be power saving, not quiet. You see, WD Greens are designed to be power saving by minimizing movement of its mechanical parts like the disk motor and the reading arm. However, when something needs to be read/written into the HDD, the reading arm has a tendency to make a sudden and violent motion as the read head moves to read the appropritate disk sector. The motion of the reading arm makes quite an audiable 'click' when it moves and this sudden movement pattern may increase wear and tear and have an adverse effect on the long term durability of the WD Gerrn HDD. Just get a more conventinal HDD to avoid these issues.
2) A higher wattage is unnecessary. You see, the PSU fans may only become noisy when the PSU is being subjected to a very high loads. (eg. A 500W PSU being used to power a system that consumes approx 480-500W of electricity.) However, the GTX 970 is quite power efficient and this system can be safely powered by a 450W PSU if the budget is really tight. You may only encounter loud PSU issues if you either buy a low quality, cheap PSU or attempt to use a 400W PSU in your system. Thus, the 500W Seasonic S12G is sufficient for your system as it is a good quality PSU and there is more than enough wattage headroom for the PSU not to be overly stressed during normal operations. If you still want an even quieter PSU, can consider the Silverstone NightJar 500W 80+ Platinum PSU for $339.
3) Good examples include the Deepcool Lucifer and the Prolimatech Megahalems. Actually, any high end air cooler will do as long as the heatsink is very large as you are going to need a very large heatsink if you wish to use passive CPU cooling. For an extreme example, check out the NoFan CR-95C:
:: NOFAN Corporation :: Noiseless Computer, Noiseless Cooler, Noiseless Computer Case, Noiseless Power Supply, and other various noiseless computer components. Specialized Noiseless Computer hardware manufacturer.
Do note that for passive cooling to be effective, there has to be good airflow within your casing as passive coolers need this airflow to help dissipate heat away and if there is no airflow, the parts will quickly overheat. This also means that you are going to have to install a lot of case fans and have reasonably good cable management (ie. not gather the cables into one lump and throw into case.) to ensure steady airflow inside the casing. Also, for good cooling of the Silverstone NightJar, you must have a positive pressure setup in order to force the air into the PSU for cooling as the PSU is fanless.
