Video cards are compatable with any motherboard that supporte the Pci-e version that the card is and the cpu will be compatable as long as your not trying to pair it with a 10 year old cpu. You also wouldn't pair a GTX 690 with an Intel G530.
So yes the 7850 will be fine with the Sabertooth MB.
The cpu is a good choice but since you are going with a Z77 chipset motherboard which supports the Pci-e 3.0 and your also going with a video card that is Pci-e 3.0 then you should also go with a cpu that supports Pci-e 3.0 and that would be the new Ivy Bridge cpu's ;
The Pci-e 3.0 has twice the bancwidth capability then the Pci-e 2.0 so the only wqay to get the Pci-e technology to work is to have all three components together , motherboard , gpu and cpu.
The power supply is junk and I won't put one on my computer so I will never recomend one for someone elses Pc. This power supply will run two video cards if you choose to have two and the rest of the Pc as well.
As far as ram goes you will not need more than 8gb for gaming and I know this because I went and bought 24gb of ram thinking I would be all set for great gaming and one day I had the resource manager open on the other monitor I have and it showed that I was only using 5gb of ram and I was playing a game at the time (MW3) , so you can save some bucks here with 8gb.