Raid setup


(╯°□°)╯︵ ┻━┻
United States
so im thinking of setting up raid, my mobo said that the nforce 4 chip supports raid, and im thinking of setting up Raid0 for now, and i have a question about how to set it up.
right now i have a seagate 12 gb sata (where i cant find on newegg anymore), and do i have to buy 2 identical sata HDD to be able to set up Raid0? or can i use an 120 gb of any HDD/ identical to my 120 gb, and use that to set up Raid0?
and im thinking of getting 2 80gb as raid0, and does the size of the HDD matter? i.e the bigger the size, the faster it loads.
later on, ill be setting up Raid 0+1 for performance and HDD failure, but if i bought 2 80 gb HDD and used that as my Raid0, do i have to have another identical HDD for the Raid1?
thanks in advance