The most important thing - and minimal thing to do - to a newly purchased G5 - is to add a second disc drive.

The software does not work well at all if you run content from the same drive as the one containing the system.

Internally - minimally - you can add a 10,000 rpm sata raptor drive
Or add a scsi card and drive.

Externally you should be looking to add a hard disc system.
External SCSI systems, are much safer at the moment.
SCSI is a well proven technology.

I think highend has put together some documentation - which is not available yet.