1) Yes the board supports SATA RAID 0/1/5/10/JBOD (Just a bunch of disks)
2) Yes the HDDs will be fine. However, consider the 1TB HDDs that have greater reliability.
3) Memory - 4 slots - DDR3 2000(O.C.) / 1333 / 1066
4) The AMD that you have chosen is Socket AM3 compatible with the motherboard.
5) Microsoft Windows 7 Home Premium 64-bit will be great.
6) Instead of getting another video card, look into some of the latest high performance video cards.
7) The 500 Watts PSU will be ok for one video card. Since you are taking a big step in your upgrade, get a Corsair HX-850 Watts PSU suitable for future add-ons. Slight overkill, but worth it. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
I am glad that you realize that RAID is not a substitute for frequent backups!