Full system back up.

I am tasked to do a full system back up. At my previous places of
employment we had a system administrator and BRMS software that handled
system back ups, but at my current place of employment I just became the
administrator (this morning) and we don't have any BRMS software. My
back up experience is limited to putting tapes into the tape drive and
occasionally adding a library to our daily backup program.  As such I
have a couple questions. The first question is how long does an entire
system back up typically take? I imagine it varies based on system, but
is there a general amount of time that should be allotted? My second
question is should I use SAVSYS, or GO SAVE option 21? In my mind GO
SAVE option 21 is what I would want to use, since I do want to back up
the entire system. Once I figure out which save option to use is it as
simple as getting into dedicated mode and kicking off the back up, or
are there any other prerequisites that need to be taken care of? Are
there any special steps I need to take to handle messages? I will be at
the console during the duration of the back up so in my mind I will be
able to handle any errors that are raised. Finally, do I need to do
anything special after the back up is finished?  Any help with these
questions would be greatly appreciated. Also, any documentation, links,
etc on this topic would help greatly. 

Thanks,

Griz