Firstly: Welcome to OCN!
I suggest looking into the ~$160 650 ti Boost. It's difficult to find a true comparison between the GTX 285 and the 650 ti Boost because of the former's age. TPU has reviewed both on separate occasions and using an entirely different test setup. Using Crysis as the only overlapping benchmark between these two reviews, the GTX 285 had 41.9 FPS
on full HD, while the 650 ti Boost scored 37.1 FPS
at the same resolution. Granted, the former was tested in comination with a E8400, while the latter was tested on a 3770k. I would assume the GTX285 achieves an FPS marginally higher when used with a more modern CPU.
Though I don't play WOW, I have read that this game is considered CPU-optimized. CPU variations should impact the game's performance to a larger extent than GPU variations. It is imaginable that the GTX 285 and 650 ti Boost's performance will be very comparable in this title.
As for the bottom clearance issue on the Node 304: you can install the PSU upside down, so it draws in air from the top and exhausts it from the side. I have tried both configurations, but can't supply any actual temperature readings for these configurations. From an entirely subjective standpoint I can say that there's no perceptible difference in sound or heat being generated. I would suggest you look into buying a 150mm or 140mm length PSU, as this allows for more room between the GPU and the PSU. I have used both the Seasonic G-series 550 (160mm) and the Silverstone ST55F-G (140mm) in my case due to waiting for an RMA replacement on the latter. With the Seasonic I had to remove the PSU bracket and mount it using self-sticking velcro straps. The Silverstone would fit fine using the bracket. When I get the Silverstone back, I will keep the bracket out and fit it with the same velcro straps, as I feel that it can exhaust out of the case more effectively because it is positioned closer to the mesh on the side panel.
To answer your question about PSU capacity: If you're sticking with the GTX 285, I'd suggest getting at least 550W. The 650 ti Boost will get away with less wattage.
Coolingwise I concur with Allanitomwesh in that it can get as hot as you make it. But there are plenty of sufficient cooling solutions available which fit in the Node 304. For comparison, I am running a 4670k @4Ghz using a Thermalright Silver Arrow HSF at temperatures of 4 degrees above ambient (idle) and 44 degrees above ambient (load). Both are well within the acceptable range of temperatures for this CPU. This is done in comparison with a relatively hot HD6950.
The only aspect limiting your choice of CPU coolers is the positioning of the CPU socket on the motherboard. Try to look for a motherboard which has the socket positioned away from the PCI-E slot, as this doesn't allow for large tower coolers to be used.
Example of a bad
Example of a good
I actually use this Asrock Z87E-ITX.