[Lagerfeldt]

Unless there's some specific reasons for it I would suggest internal drives. It's usually slilghtly faster and often more reliable than any external solution, YMMV of course.

Keep your system on the first disk, libraries on a second disk, projects on a third disk.

I like to do manual backups and not rely on any automated process. I make physical copies of the most important stuff to spanned DVDs which are archived and at the same time a copy on an external hard disk, the less important stuff is only backed up on an external hard disk and most of it overwritten later.

The system disk should always be journaled of course, but depending on what DAW you're running you can disable journaling for up to 20% performance increase (via the Disk Utility). I've done this on my project disk which increased track count from around 100 to 120 tracks of separate individual stereo audio at 24bit 44.1 kHz.