Backup might be OK, you just let it run overnight.
Restoring from backup, in an emergency, will drain your patience. Stick
with SCSI drives if you can (for this machine, you can also get IDE accelerator cards and use internal IDE drives).
USB 1 is going to be hard to add to this machine; lots of cards that claim
to work with OS 8.n have fine print that says "PCI 2.1 required" which
means they only work with blue/white G3s and later. Which already have
USB 1, of course. Sonnet Tango is one card that should work, for USB 1
operation only. The USB 2 speeds require OS X, 10.3 I think.
Firewire (the Tango card comes with firewire too) is faster for almost everything, and has most folks' vote in the Macintosh world. I know it
has mine.