Moving your thread to the appropriate forum Jay.
Largest capacity would be 50gb (nominal). The 50gb disks are extremely expensive however. DVDs will be much cheaper per gb storage space.
Life expectancy is unknown at present. A few of us are currently avoiding Ritek BD-R disks because of some reports of them losing data over time. (they are sold under various brands, like Ridata and Memorex)
The safest bet is probably to use either Japanese made disks, like Sony or Panasonic, or if you want cheaper Taiwanese made media, stick to Verbatim. The current burner of choice is the Pioneer 205.
Personally I think that hard drives make more sense for general data storage. You should always make several backups for important data of course...never put all your eggs in one basket in other words.
Blu ray disks are only necessary for backing up blu ray video to play on stand alone blu ray players, but that is just my opinion.