pretty decent 10 phase powers, lower rds on mosfets.
and for memory you will need ddr3 1666mhz ram dual channel kit.
if your gonna be using 4gb or more of ram you will requre 64bit version of windows 7. always best to use 64bit and yes its compatible with the selected hardware.
and your question about sata2, yes your current harddrive will work fine, sata300 is 3gigabit bus 350mb/s all it means is it’s a higher bus cap than sata 1.
I agree with Bob, asus is like nokia and got their reputation from their tag, I would also suggest MSI for a motherboard, gigabyte merged 2yrs ago with asus so I wouldn’t put gigabyte past anything myself