Most modern mobos support crossfire/SLI so I don't that is going to be much of a problem.
I personally believe that 1 good graphics card is better than two anyway.
It would be useful to know what sort of budget you have and you might want to look at a CPU/mobo bundle with I suggest at least an i5 CPU.
RAM and PSU are probably fine.
I'll do a little research and post back with some idea of what your components are worth but do not expect to much.