"what happens in RAID5 if one drive fails?"
There are three or more disks in the array and the data is protected if one disk fails.
"and what happens in RAID1 if one drive fails?"
The data is safe on the other disk as the data is 'mirrored'.
But having read your post, I was struck by the fact that, other than your DVDs, you haven't mentioned backing up your files. While a RAID array does that to an extent, it's no substitute for proper backups. I think you need to consider that, more than adding more arrays. Are some of the drives you list, external drives, or are they all internal?