MRTG

I am new the MRTG world and I'm successfully monitoring a few devices
and will be adding many more.

I currently use the command:

cfgmaker --global "workdir: /var/www/mrtg" -ifref=ip --output /etc/
mrtg/mrtg.cfg --global 'options[_]: growright,bits' public@localhost
public@192.168.1.4 public@192.168.1.5 public@192.168.1.6

and then:

indexmaker --output=/var/www/mrtg/index.html /etc/mrtg/mrtg.cfg

This works great and gives me all my devices in the /mrtg html page,
however I'm unclear of really what I'm doing here. Also if I am to
add new devices do I have to append to the above command, or what's
the best way to add new devices the configuration.

The above command is only monitoring traffic, what would I need to
monitor CPU Usage, Disk Usage, etc...

Thanks