Could I do 3 500GB in a RAID 5, or RAID 0, and set up my 1TB as a RAID 1 redundancy type thingy? (I know I'd need 1.5TB if 3x 500GB were in RAID 0) But yeah...because I sense that a RAID 0 array is prone to failure, because it just takes one block (I'm not sure on that) to be corrupt, one drive to fail for them all to. I like the added benefits of speed, but I think it's only worth it if I can rebuild the array should it fail.
What you need is a backup program, not another RAID solution.
There is NO RAID SOLUTION ON EARTH THAT MAKES A GOOD BACKUP.
Buy Acronis True Image, and configure it to back up the information on your RAID array to the 1 Tb drive.
What do you want the 3x500GB for? If you're thinking about putting OS+app on a RAID5 array, don't even think about. Even on my server-class hardware RAID card I don't do it. RAID5 is for storage only, any speed gained is just a bonus.
If you were to put them in RAID0, besides ~60GB being used up by the OS+app, are you going to put your data onto the remaining space??? I could see the excess being used as temp. storage e.g. scratch space for editing HD footages, but besides that, not much use.
Or you could grab another 500GB to make it 4x500GB RAID10. Then you can put both OS+app and data onto it with both speed and reliability.