I woukd suggest doing journey maps of a user outside of your system too. Helps understand the use cases easier.

An example: If a user exports data where does it go after? What do they do with it. Can you collect artifacts or video of users showing you this?

Again wish there was examples.

We did these for only three clients. User Journey Maps are time consuming and I would recommend focusing on a key group or task to start. I think it took us 3 weeks interviews and another 2 weeks to create the deliverables. Despite the time, we got great insight on the mindset, context of the situation, pain points they endure, and it sparked ideas on how to improve it.