I would recommend spending your $$$ in the following order:

1) As much tape space as possible - both slots and tape capacity
2) As much hard drive space as possible
3) As much memory as possible
4) Worry about more than 2 drives after taking care of 1-3

I can speak from experience - I had a 14 tape DLT library and 33 data tapes.
This left me with a lot of work every day swapping tapes and managing the
reclamation of the tapes. If I had gone with AIT this would have been
better - but not great. I would have had 14 slots and 15+ data tapes. Do
yourself a favor and buy 10 times the capacity you need and go with the
AIT - you'll be glad you did. If you get less than 2 tape drives you'll hate
life. I had a broken tape drive leaving me with just one for a couple of
days - I bought the repairman lunch when he showed up to fix it.

Ron James