it's really up to you. i believe that EJBBase provides default implementations for some of the methods required for the interface, so if you want to leverage that, go right ahead, otherwise, you have to provide the default impls yourself.
pls make sure you normalize any fields that may link into the core tables, etc (you may not have this, but if you do). the wiki pages should document how to use the existing ejbs from the core so you don't have to duplicate that functionality.
The persistence of your module is defined by you.
You can use anything you want EJB, JDBC, Hibernate...
You can look at the existing modules they use org.jboss.nukes.core.ejb.EJBBase but you don't have to.