Well to start, that board will be horrible in Crossfire. The second PCIe slot only runs at 4x, which would cripple the GPU. And the 600W would not be able to handle 2 5870s in Crossfire. You might have trouble with a 700-750W.
That said, you shouldn't need to Crossfire down the line. By the time you'll really need to start thinking about it, you should be thinking about a complete upgrade.
RAM: Corsair XMS3 2x2 GB 1600 mhz CAS latency 7 $110. Cheaper for the same specs.