I am new to the Elastic Stack, so far it has been super-fun to learn. Thanks for making this great toolkit available!
When getting started, I struggled with a number of newbie mistakes. There are quite a few things which need to line up in order to get your first bit of data to appear in Kibana.
Of the mistakes I made, one seems easily fixed. I was pointing to files which the logstash user didn't have permission to read, for example /var/syslog and /var/log/apache.
This is logged with something like:
[2016-12-12T20:59:26,648][DEBUG][logstash.inputs.file ] _globbed_files: /var/log/apache2/access*: glob is: 
I would suggest logging a warning, when the glob array is empty. I can't see to many cases where "glob is: " is anything but bad! It could say something like "Perhaps you mistyped the file path, or you lack permissions to read that file." It seems like it would be an easy addition to logstash. It would definitely have improved my initial experience.