Don't worry about OC'ing it, it'll OC just fine if that is the Intel Liquid Cooling solution (which google said it is).
The Antec 900 is a good case, but any mid or full ATX tower case will work, but don't just get any cheap one cause you DEFINITELY get what you pay for, so spend at least $60 on it!
Get a Corsair or Seasonic PSU with at least 600 Watts, but I recommend 750W.
For a Gaming PC, your GPU really should be the most expensive part. Tom's did a review and recommended the most bang for buck on video cards in each price range. here's the article. I would say anything above $200 will be okay for that PC, but I would personally pair a GTX 670 with it.http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-5.html