The fewer the partitions the better, in general, I'd say.
Whenever I divvy up a drive into many partitions, I always end up un-partitioning it later. You just can't predict in advance how much space you'll need for DV, mp3, applications, backup, etc.
The only partitions I'd really suggest are:
* a small ~1gig partition for Classic & your classic apps.
* a medium ~8 gig partition for OS X, apps, and your non-media (small) documents.
* a big partition for all your media files. It's easier to have these separate so you can reinstall OS X cleanly if you need to.
I think that'd work fine.