Hi!
Regarding question 1 there is a log of Filebeat printed every 30s that can give you the overview of how many events/logs have been shipped to the ouputs. An example:
2020-07-16T11:09:08.667+0300 INFO [monitoring] log/log.go:145 Non-zero metrics in the last 30s {"monitoring": {"metrics": {"beat":{"cpu":{"system":{"ticks":88,"time":{"ms":6}},"total":{"ticks":359,"time":{"ms":52},"value":359},"user":{"ticks":271,"time":{"ms":46}}},"info":{"ephemeral_id":"0e4cacc1-264f-445f-a893-2403f151b170","uptime":{"ms":150035}},"memstats":{"gc_next":48353472,"memory_alloc":24227664,"memory_total":65300608,"rss":827392},"runtime":{"goroutines":43}},"filebeat":{"harvester":{"files":{"2872277f-453a-4b46-9416-a2e696cef4dd":{"size":290}},"open_files":1,"running":1}},"libbeat":{"config":{"module":{"running":1}},"pipeline":{"clients":2,"events":{"active":4117,"retry":50}}},"registrar":{"states":{"current":2}},"system":{"load":{"1":1.8828,"15":2.2056,"5":2.0996,"norm":{"1":0.1177,"15":0.1378,"5":0.1312}}}}}}
With this looking at the events field you can take away the Filebeat's performance.
About the 2 other questions I think you should redirect them to the Logstash forum so as to have an answer from Logstash folks.
C.