This is highly dependent on your business needs and the needs of the individuals or teams who will be performing the monitoring. There is not really a "one size fits all" or even a "best practice" for monitoring in most cases.
There is an excellent reply by Garin Walsh in the following thread which discusses this in some detail:
Tricky question, what do you monitor? Has anyone found a way to answer this?
What it comes down to is that the stakeholders involved who are familiar with and/or responsible for the SQL DB Servers will need to be consulted to determine what information is most valuable to them. This will vary greatly depending on the nature and needs of the business.