Debian is a bit of an odd beast. Generally, you'll need the first 2-3 binary disks. Beyond that, it really depends on what you want to run.
Unfortuantely, I've never been able to find a manifest of what's on each disk, but *shrug*.
I've not run Debian on HP-PA before, only Intel, and I got away with the first 3 disks. I suggest getting the first 3-4, and then use 'apt get' from there.
One long-haired git at your service...