Yeah, the psu looks fine and I'm not totally sure about the 4-pin molex. My Asrock motherboard has the molex specifically for crossfire but on the other hand I have another motherboard that is decked out with 3 7950s all on the x-1 to x-16 risers and it doesn't have the molex on board. There are a lot of places you can get the riser cards from ebay so it won't be hard to get good cheap risers. The main thing you will want to pay attention to is how fast you need them. I for instance bought mine for like $3.75 shipped but they came from somewhere in China I think. Anyways it took about 8 to 10 days total for me to receive them but they worked without any problems. So if you need them faster make sure you buy from inside your country even if it costs you a little more.

Searching this is ebay gives tons of results: New PCI-E Extension Cable 1X To 16X Riser Extender Card