It would be better to get a stronger single card then to crossfire to weaker ones initially. For around the cost of two 7770's you can get a 7950, which I am fairly sure will outperform or at least match the dual 7770's.
This is the difference between the Phenom II 965 and the 8350.http://www.anandtech.com/bench/Product/697?vs=102
Though as I said, the 8320 is a good option. Hardware wise it is identical to an 8350 but lower binned (lower quality essentially) so it supposedly wont overclock as far. If you do get the 8320, you could probably clock it to 8350 performance quite easily.
Its all good, better that you voice your questions here than go out and make an uninformed decision.