Configuring Power MAC G5 For Final Cut Pro Workflow

I am new to MACS as most of my experience has been with windows OS. I recently took some classes in video production (which initiated me to the MAC environment) but abandoned it due to frustration caused I believe by under-resourced computers in our lab (Mac Pro w just 3GB RAM running Final Cut Pro X) too many hours wasted watching the rainbow windmill. My offer to buy 16GB of RAM and loan it to them for a test was rejected.I want to continue working on video editing, so found a couple Power MACs and FCP v5.1. One is a 1.8Ghz dual (bought before I knew better) and the other a late 2005 Quad which I am configuring for editing. It currently has 10GB or RAM and I expect to bump that to the 16GB limit. The hard drive space shocked me. Who would design a case like that to hold just 2 drives? I see that additional internal drive cages are made by 3rd parties and am considering that. But before I get too involved, I need to learn more about MACs.I obviously bought these used and didn't get any install discs. There are 2 drives in the Quad. A 500GB holds about 100GB for the OS and applications. The second drive is 250GB and empty. As I understand it, the Quad supported only SATA version 1 (150MB/s) correct? Will it support 2TB drives?

I'd like to separate the OS and APs from the data and think that the 250GB drive would suffice for that purpose. Can the files on the boot drive be cloned to the 250GB drive so I can use it to boot from? In the alternative, I might replace both with 2TB drives if the OS (10.5.8) will support that. The primary concern here is to keep all the existing APs functional.I am just now taking a linux class and the advice there is to create lots of different partitions. Onr for the kernel and system files, another for APs, etc and to create a swap file on a different drive for optimal performance. I think that would be the same for the scratch file for video rendering.

Aside from the 2 HD bays, I am studying the idea of a SATA card that would support internal as well as external sata devices. Given that rendering is processor-intensive, is there any advantage to adding a SSD via a SATA card running at 3 or 6GB/s? One reference I read indicated that the video can't be processed faster than the existing HDs can take it. If true, then I wouldn't see much advance in adding faster drives. But if someone that ahs experience with such, I'd like to get some input.As to the 1.8 Dual G5 that I grabbed before i 'discovered' the Quad, I'll probably use that more for video capture since its PCI-X slots will accomodate my video capture cards inputting mostly miniDV tape media.

Info:
Power Mac G5 (Late 2005), Mac OS X (10.5.8)