Logstash Monitoring APIs

I am trying to use the monitoring APIs to determine if the logstash server is performing well and processing the input. What are the data that you would track to identify this from the API outputs that we get from Monitoring APIs?

I will be monitoring
heap_used_percent
cpu load_average
events - filtered, out and in
grok filter patterns - in and out

What else would help determine the health of logstash?

Any suggestions?