SATA II, will fit in that motherboard, don't worry. SATA II is also backwards compatible with SATA I.
Yes...it's possible to add another hard drive to a RAID array. But I'm not sure about three hard drives for RAID 0, will work. I think it's recommended that you use the same size and cache hard drives, for a RAID setup, to avoid conflicts. But you could use hard drives of different sizes, for a JBOD(Just a Bunch Of Disks).