OS 10.2.6 on a G4 Cube, External FW Drive Maxtor 5000

I started my backup to my external drive and went down to watch TV
6-3 hours later I am back and I have my nice 'Planets' on my screen..
everything is quiet... I move the mouse to wake up my computer... no
way
cannot put it back at work.... I have to shut down... (Energy saving is
off in my preferences, so I don't understand why the screen and the
disk were on energy saving)
On Reboot , as always, it wait for local disks but doesn't mount the
external FW... wait is very long so I shut it down (2 time) and
disconnect the external FW drive..
on reboot I get the grey screen with 2 larges whites strips on the
screen.... I have to reboot again (3rd time) and it works..

I also understand why I have so may failed reboots , I need to remove
the private/var/db/Bootcache.playlist to get a correct one.. (what is
this file ?)

i try to understand the system.log, but it's impossible to detect
what's wrong (I am a simple user, not a system manager !)


questions
1 - what should I do to avoid so many reboot problems?
2- what shoudl I do to avoid so many problems with FW external drive
when I have to shut down and reboot ?