unlike logstash where you installed logstash and then used/added plugins, is it the case that beats are self-contained?
Yes. A Beats-based binary is typically statically linked with an on-disk footprint of maybe a few tens of megabytes and a RAM footprint of a few megabytes.
I hope the file beat can well handle rotating-file logs and it is not too beta.
What gives you the impression that it's beta software?
Perhaps I am not used to elastic documentation but it is hard to fine documentation / configuration instructions for the file beat....
If I google "filebeat" the second hit is https://www.elastic.co/guide/en/beats/filebeat/current/filebeat-getting-started.html. Were you not able to find that documentation or was it hard to understand?
and I find it baffling why would you forward beat information to logstash not directly to elastic as mentioned on the website....
Logstash is able to process events in various ways that neither Filebeat or Elasticsearch is capable of. You typically don't send the raw logs to ES.