Now that you are switching to a MDD FW800 PowerMac, you have the space to install up to four 3.5" internal hard drives. If your FW800 PowerMac is like my MDD when I got it, you might need to find the drive cage that fits under the optical drive bays, to hold two more hard drives. It is the same cage as the one that holds the hard drives vertically behind the optical drive bays, but it fits under the drive bays and holds the hard drives horizontally, not vertically.

My MDD had the IDE cables and power cables required for the two additional hard drives, but not the cage, so I don't know if the cage was removed by the previous owner, or if it is an optional part that you have to specify when you order your MDD, or FW800 PowerMac. I found and bought my drive cage from someone on eBay for $10 to $15, IIRC, which is probably a high price for that part, but if you can't find it anywhere else, what is a guy supposed to do. Since it is exactly the same as the other cage, and is removable from the rest of the computer, if you find an MDD that has been junked and is being parted out at some computer recycle shop, you can just grab the hard drive cage that holds the drive vertical behind the optical drive bays, and use it in your MDD for the drives you want to install horizontally under the optical drive bays.

My point in this whole reply, is that you should not need any external storage through FireWire to E-SATA connection, except for making backups that you can put away in a separate location from your computer, in case of fire, or some other catastrophe that destroys your computer and ruins all of the drives inside of it.

As far as external storage for backup purposes, I just bought a USB3 1.5TB external drive to use exclusively for backup purposes for 3 of my Mac computers, my G5 PowerMac & two G4 PowerBook's. It is backward compatible with USB2.0, so it works with all of my computers. The only drawback to it is that it draws its power through the USB cable so it will not work from a G4 PowerBook USB2.0 port, because the G4 PowerBook USB2.0 ports do not provide enough power to run external USB hard drives. So, I have to use a powered USB hub and I could only find one of my two powered USB hubs which I think might be only USB1.1, not USB2.0, because it took several hours to backup about 120gb of data.

I am using Time Machine to backup those 3 MacOSX10.5.8 computers. I need to check to see it Time Machine backs up other partitions, and/or additional hard drives that are not formatted as Mac hfs+? I doubt that Time Machine will backup the other partitions, or drives that have different OSes on them, in a dual or triple boot setup.