RAID 5 has the advantage of faster reads, but you take a hit with slower writes since you're also having to write parity data. RAID 1 is easier and you get at least the same performance of the single drive.

My primary server at home is RAID 1 and my performance desktop is using RAID 0. RAID 0 offers performance by striping the data across multiple spindles, but you lose everything if 1 drive in the stripe set fails.

Using a DVD burner for backup still would require the user to change media even if you schedule the backup. RAID will protect your data in the event of a drive failure, but it won't help you in the event of data corruption. Regular backups could allow recovery to a point in time before the data was corrupted.

RAID 1 with an occasional backup with something like a Maxtor OneTouch II should give you the belt and suspenders.
PCmag: Maxtor OneTouch II External USB Drive

There's also a really low tech way to keep an extra copy of important data. Schedule an event that copies the important stuff from your primary data source to another system on your network. Chances are, both systems won't fail at the same time.