As far as mobos go, I've had really good luck with both ASUS and Gigabyte and wouldn't use any other brand at this point.
You are made of money, so get at least a 940. Everything above that is kind of pissing money away, comparatively.
I'd get at least 8 GB, 12 if your mobo supports it. At /least/ 850W.
A solid state OS drive is a good idea, I want that on my next build. G-Skill makes a good one.
I think that in CrossFireX, two 5850s and two 5870s are comparable. Since the 5850 is $100 cheaper each and more widely available you probably want to go with it. Alternatively, just track down a 5970 and save yourself the trouble.