The most power you'll need for a signle 770/780 is a solid 650w (XFX/Seasonic high efficiency rating) or 750w max.
Note: Corsair CX power supplies are cheap and known to fail under extended periods of high load. Not good for gaming/performance rigs.
Sabertooth mobo is a huge gimmick and actually hurts thermal performance at times. Toms and a few other tech sites have info about these. Don't get sucked into the sleek black bs, any decent manufacturers Z87 will do just fine.
The sweet spot for VALUE (ie. performance per $) is around $1500 for all hardware (excluding peripherals). Diminishing returns go way up after this point. This is why the jump from 770 to 780 is a real bad [economical] decision, the marginal cost vs. marginal benefit to performance is far from worth it, compared to going from the 760 to 770 for example. I am at work and unable to provide the exact #'s but I have done relative price/performance comparisons for each tier of upgrade in gpu's - you can too - and it isnt worth it.
Case is entirely your decision, not really worth taking peoples advice here because it is more personal than any other component. Many people love Antec 300's, and certain Fractal/Corsair cases that I never liked, so I went with a Carbide 400R because it suited me. Besides the front panel I/O's you want, airflow considerations and space for chunky cpu heatsinks (air coolers & radiators alike), its a complete crap-shoot.