loosing power while writing to a HDD will lead to data loss and might even damage the HDD.
if you live in an area that has power outages you should invest in an UPS.
Yes losing one drive on an RAID1 will allow you to access the data from the other drive and you do not need to backup to a third drive to restore the RAID array.
you mother board has six SATA ports to build you RAID use PORT# 2+3. Port #0+1 might not work if your are booting of the IDE