It sounds like you are well on your way.
This log gives you the opportunity to review the process after completion. For example, you might look at like #1 of
usage_events_20160515.log (which will now either be in your "archive" or "reject" directory, as indicated a bit later in the file). The line probably references a client fetching a non-ojs file, and thus the warning would be harmless. If the line references a OJS article instead, you would want to carefully look at the URL to determine what makes it different (and prevented OJS from processing it).
If you see a line prefixed by "[Error]" in this file, it indicates something went critically wrong and requires review. In the event of an error, you should receive an email notifying you of the need to review the logfile.