In my experience, the document content model in Alfresco does not adapt well to the relational database paradigms. Although you may adapt most of the relational DB concepts, Alfresco is not really designed with that purpose in mind. After completing your content model using ERD and RDB concepts, you will probably realize that performing some relational queries can be difficult or impossible, and the performance of some queries can be very poor.
I don't have a methodology of my own, but I have found that you may benefit from abandoning, at least temporarily, your relational DB experience, and trying to understand and embrace Alfresco's model.
You may feel uncomfortable abandoning the RDB paradigms, but the Alfresco content model has interesting features that a RDB doesn't have. The content model is conceptually closer to Object Oriented Programming, Aspect Oriented Programming, and hierarchical databases.