Yes, you can do it that way: set maxscratch=0 and manually define tapes.
Yes, collocation will behave with a less than ideal number of tapes, placing
multiple clients per tape.  What I don't know is if will be smart about tape
mounts in that situation.  I'm guessing it won't be smart.

I would add one wrinkle to your environment to ensure you don't get the
dreaded, Server out of data storage space message as you consume all of your
tapes.  Create a second tape pool and make it the target of the first pool's
nextstg parameter and set the migration threshold to 99%.  That way, if you
should run out of space, a simple migration process will start.  Once you
detect this has happened, you can simply add volumes to your first pool and
issue move data commands on the volumes in the second pool.

The trick is in the analysis of what the correct number of tapes is.  You're
on the right track.

Kelly J. Lipp
Storage Solutions Specialists, Inc.
PO Box 51313
Colorado Springs CO 80949-1313
(719) 531-5926
Fax: (240) 539-7175
Email: lipp AT storsol DOT com or lipp AT storserver DOT com
www.storsol.com
www.storserver.com