OP here, I appreciate the feedback! I tried to focus on things which could take down your database, so things like particularly slow reads and writes, autovacuum settings, reducing lock contention, particularly focused on cases that I've seen. There are lots of things that I left out which would belong in a general user guide.

We're heavy users of stored functions because we're (perhaps overly) reliant on Postgres triggers, which can improve performance by reducing network round-trips but are fairly risky because they're difficult to monitor and observe.