The details concerning my answer are available in my post: http://wolfcrow.com/blog/computer-for-video-editing-part-one-listing-the-basic-requirements/In short:
If this is a money-making professional machine, a dual Xeon
64 GB RAM ECC
If not, then an i7 3930K, same RAM except no ECC, GTX 680 (4 GB version) or Titan
An HP Z820 or Dell T7600 is perfect. I'm getting a Supermicro build (dual Xeons, E5-2630), which is just as good.
I wouldn't get the U2713, it's not the same as the U2711, which is what I'm getting. If color is super critical, an FSI 17" monitor is good. I'm more into video, so the U2711 is still only a GUI monitor.
Whether or not it's overkill depends on the kind of files, photos or footage you work with. For Nuendo it's definitely overkill. If you're running monitors, you'll need an audio interface like the ones M-Audio makes. I'll probably get that or a Mackie. For monitoring I'm getting Yamaha MSP3, which is cheap but excellent for a one-person station.
For streaming I recommend dual Xeons and fast arrays. I like RAID 1 (2 drives) and RAID 10 (4+ drives), and I tend to stay away from parity drives. Software RAID is fine unless you are transporting heavy files on a regular basis.