Case and PSU for gaming rig i5 3570k, HD 7850

Hello everyone, this is my first gaming rig build and I need help picking out good case and PSU for the rig. Specs are:

- i5-3570k (planning to OC moderately like 4.2 - 4.4)
- AsRock Z77 Extreme4
- Msi 7850 Twin Frorz OC 2GB (factory overclock 900Mhz - planning to OC to its most potential or maybe going Xfire if future games require so)
- Corsair Vegeance Low Profile DDR3-1600 2x4GB
- Samsung DVDRW
- 1TB WD Blue
- 128 GB Samsung 830 SSD


My budget is about $100 for each of them (not strictly though, can go a bit over if need be but I want good quality parts that can handle the job fine with price as low as possible)

- Case: Good airflow, roomy enough in case I decide to go Xfire in the future with good cable management.

- PSU:

+ PSU for CPU OC and GPU OC (some that I have in mind are: Antec HCG 520w, Seasonic S12II 520w, XFX ProSeries 550W Core Edition. Is 520w enough for my CPU and GPU OC?)

+ PSU for CPU OC and Xfire ( How much wattage should I choose? 650 or 750?)


Thank you for your help.