I completed the configuration & monitoring chapter. Postgres allows configuration modifications while cluster runs by means of ALTER SYSTEM command. Modifications applied this way will be appended to postgresql.auto.conf file.
You can use configuration generators like PgConfig with simple GUI interface.
Information about running queries, sessions and backend processes can be read from pg_stat_activity catalog. Information about locks lives in pg_locks catalog, while pg_stat_database includes data about COMMIT and ROLLBACK transactions. You can check table and index usage in pg_stat_user_tables and pg_stat_user_indexes catalogs.
All build-in statistic catalogs show real-time data. For persisting historical statistic you need to install pg_stat_statements extension.