First things first, you'll need to back up any data that you wish to keep, because you must reformat your drives to create a RAID array.
It's impossible to say what the best RAID level would be for you, because you never actually told us what your application was. If you're looking for more storage plus redundancy, then yes, RAID5 would be a good option. I'm gonna get a little "RPG" with my analogies here, so I aplogize
RAID0 will give you +storage and +speed
RAID1 will give you redundancy (NOT TO BE CONFUSED WITH BACKUP *)
RAID5 will give you +speed, +storage, and redundancy (Speed increase will be very small, if any. Can even decrease performance in rare occasions, but I won't get into it)
RAID10 will give you +speed, +storage and redundancy
Pretty much that's what the "popular" levels or RAID are. There's more out there, but none that you really need to know about.
NOTE*: RAID is not backup, and should not be considered backup. RAID does not protect against data corruption, accidental deletion, damage due to viruses, and the like. RAID [with redundancy] ONLY protects against drive failure. If you're just wanting to back up your data, buy a separate drive, back it up, and store the drive in a safe place off site.