Hi,
  We are using optical juke box. and we find it fair enough. Having worked
with tape spools as well. I am inclined to say that tapes are more prone to
error than optical disk volumes. The sizing can be done by the amount of
data that needs to be sent. The juke boxes that we are using is a 3995
library a c64 model . You could go until atleast 670Gb.

As far as the applications are concerned I am not the right person to commit
about it. But as far as I know any flat file can be dumped on to the storage
area with the aid of the ADSM client.

I would also recommend you to upgrade to at least 4.1.5 or beyond.
and also size your disk storage pool.

regards

Sri