You do realize Nagios comes with a load of pre-written scripts (in my case /usr/local/nagios/libexec dir) official plugins page http://nagiosplugins.org/man
and more are avail from http://exchange.nagios.org/directory/Plugins
Specifically for your qns:
1. cpu; given how much cpu percentages rapidly vary over very short times, you would be flooded with alerts.
I recommend check_load instead
2. I didn't know disks had an idle mode ..
Official Plugins HOWTO guide http://nagiosplug.sourceforge.net/de...uidelines.html