ASrock used to be owned by ASUS, they split off a while ago, hence the similar names. They were their 'cheap' brand but have come to surpass ASUS.
Honestly ASUS is horrible. I've been going back and forth with them for 10 months on my ROG motherboard. From trying to charge me to fix something in warranty to getting a board with obvious physical damage, to being ignored completely I wouldn't touch them with a 10 ft pole. I've heard nothing but good from ASrock, they seem a very solid choice, only reason I didn't go with them is because I didn't like their color scheme.
As for the GPU, I wouldn't bother getting a second one later on, the 1GB of VRAM will be a bottleneck. I go up to 1400mb on my single monitor quite often.
I would suggest paying a little extra for a good 6950. I had a GTX570 but between having a few driver issues and running out of VRAM, I cut my losses and moved back to AMD.
Your mileage may vary, a lot of happy NVIDIA owners and most people have no driver issues on both sides.
Other than that you have a very solid build, normally I would recommend a cheaper PSU, but I had an XFX fry most of my last rig, Corsair is known to make some of the best PSUs and stand by them so they are worth it.
Enjoy your new rig.