%WQhcO8dY0yn90ppwpd0vf7LaSuDY3yACsQz9Fgw8uz8=.sha256@ev the log is the offset.log file and is the master db in flume. All other ones are optional.
Here's a repo with some other flume stuff and showing it progressing in complexity. : https://github.com/mixmix/ssb-server-plugin-intro
Unfortunately is focuses on flumeview-reduce which I wouldn't recommend so much. It's a good starting point but I think it's also a bit of a hog. Flumeview-level (or flumeview-query, and ssb-query which are both built on flumeview-level) is the bomb.
I made some diagrams about how these things work:
flumeview-reduce: %jD+Zl3O...flumeview-level: %QnST4gi...