Just go RAID 5 or 6. RAID 5 will allow 1 drive to fail without losing your data, RAID 6 allows 2 drives to fail and the first failure will not impact performance. I would just do 1 big RAID 5 or RAID 6 array if I were you.
RAID 50 will required 2 parity drives just like RAID 6, but if 2 happen to fail in the same stripe, you're screwed. The benefit of RAID50 would be a little faster write performance but thats not really important in your application.
If you have the card already, otherwise you can save serious $$$ by using SPM39x series controller