What is the best design research method for multi-users products? [on hold]

The idea is to design a “Multi-Tenant” product that enables various types of users to configure the UI to their needs (e.g. Salesforce). I am interested in receiving information regarding design research methodology for these kind of design tasks and to understand how (if at all) it differs from the known User Centered Design approach. e.g. how to handle the following challenges: - There can be hundreds of types of personas. Is there a point to define various personas at all? - There can be endless types of design permutations that can be configured. What can be the recommended design analysis method that will conclude the optimum design framework? - What are the design deliverables for these kind of projects? (a widget library? Recommended templates? Etc.)