No, it is not about assigning step number in PFCG. You create a different step for each role in the workflow step definition activity. Then, in the BRF+ application, you need to route the CR to that specific step. To route based on material types, you need to enhance the BRF+ application by adding the material type field. See this document: How to-Master Data Governance for Material: BADI USMD_SSW_RULE_CONTEXT_PREPARE to Enhance User Determination
Then, in the CR step properties activities, you can assign different UI configurations to that step. So, when the CR is routed to that step number, the specified UI configuration is displayed for that user. I don't have access to a system at the moment so I can't add any screenshots.