Have you maintained code bases not written by you much? Have you worked in teams of 10+ people long enough to see people leave the company?

You can never write down too much. Please * write meaningful JIRA descriptions and try to have PRs linked to the ticket * always have a README.md that explains how to build/run/deploy the service * create and maintain a runbook document (another md file?) with frequently used commands and hints at debugging previously observed problems * add comments on class responsibilities and business rules * have a few unit test-like "tests" that make the service execute its main flow