Hi Renvik,
I've worked on workflow-heavy business applications in Mendix, and the biggest lesson was to design the process first and the pages second.
For your use case, I would start with:
For document management, I would leverage the standard System.FileDocument model unless there is a strong reason to build a custom storage solution.
For integrations, keep external-system logic isolated behind dedicated microflows or modules. It makes maintenance much easier when APIs change.
One mistake I've seen teams make is trying to automate everything in the first release. I'd start with claim tracking, task management, and role-based access, then add reporting, notifications, and integrations incrementally.
For non-technical users, simplicity usually wins. A dashboard showing "My Tasks", "Pending Claims", and "Items Requiring Follow-up" is often more valuable than a feature-rich screen with dozens of options.
Mendix is a good fit for this type of application because workflow, security, document handling, and integrations are all areas where the platform is quite strong.
Hope that helps.