Monitoring your network and hosts is gathering and honing the tools to “walk the wall” so we can sleep at night.
At minimum, you should review public announcements from the hardware/software vendors, as well as from security related organisations.
Remember that you have a lot of independent/inter-dependent tools deployed on your site(s.)
There are numerous tools in the ports tree for monitoring, managing host configurations. Our primary tool of choice is:
As a network expands, vagaries in performance requires a lot of data to more readily diagnose, assess.