Are you referring to building a Management Information System? I wasn't sure what MIS stood for, but that seems to work.
Customer journey mapping is great for having a very high level perspective on the whole process, especially where you need to communicate findings—and how they relate—to other team members and stakeholders.
Seeing as you're in the discovery phase (and exploring and open to new ideas), and looking to develop a wide view, I'd use a mix of formative and summative methods. For example:
- Contextual enquiry or user interviews (rich, behavioural data)
- Traffic analysis & metrics (behavioural, quantitative)
- Something else, as relevant. ie Card sorts, surveys or diary studies to develop mental models (attitudinal)
It's hard to say without knowing more about your project, but the above (or similar) will get you in the ballpark.
You'll probably want 4 inputs minimum, and at least one of those needs to explore the MIS territory from a strategic perspective.
How do the four products relate? What kind of brief did you get?