1. Does the 4x4GB have the same CAS Latency as the 2x8GB? What are the timings?
2. Go with an OCZ Vertex 4 SSD. Also, go with the 2x2TB WD Black rather than the 1x4TB WD Black.
3. Active PFC. Make sure it's >= 80 PLUS Bronze Certified. Also, make sure it's powerful enough: http://www.extreme.outervision.com/psucalculatorlite.jsp
4. If Linux is not an option, then I'd stick with Windows 7 if I were you.