Firewire / USB
You don't need Firewire for a good external drive, USB is just as good.
A decent USB 2.0 hard drive is good, there's no doubt, but in the countless situations I have used a USB 2.0 AND a firewire 400 drive, the firewire is allways faster at nearly everything.
I work in video and am constantly chugging large, multiple files around and when someone brings me a USB drive to transfer from onto my firewire drive, I set it going and leave for a two week holiday while it does it thing
But, yes for normal everyday music, photo's documents USB 2.0 is fine.
Just thought I'd add my penny's worth
Anyway, with a 64Gb SSD drive, sure space is at a premium, but along with a time capsule, backup is easy peasy!
Mel