Which CCMS Monitors are most essential?

I am starting to map out a monitoring strategy for our company. I would like to start by activating the most essential CCMS monitors which can be used across all of our current SAP solutions with agents installed on them such as CRM, SRM, XI, ERP, and SolMan. I have availability up and running on all of them, but want to know which other monitors are most critical for checking performance statistics, free space, cpu usage, memory allocation... etc.

Are there any particular monitors that are part of a best practice... should always be enabled for critical system monitoring.