The JBoss 'all' server setup starts up a clustering as a default. But I guess 'all' contains plenty of unnecessary services for a web application based on EJB3, JPA/Hibernate.
What is the minimum setup for JBoss with JBoss Cache clustering?
Depends on what you want to cluster (replicate state, that is).
HTTP sessions: jboss/server/node/deploy/jboss-web-cluster.sar/META-INF/jboss-service.xml
EJB 2: .../server/all/deploy/cluster-service.xml
EJB 3: .../deploy/ejb3-clustered-sfsbcache-service.xml and .../deploy/ejb3-entity-cache-service.xml
If you remove something, that is needed by something else, JBoss should complain after the startup finished.
I'm not sure what the minimum would be in your situation, we don't use the clustering option where I work. However, the only way I could come up with to minimize our setup was to undeploy everything but the services I knew we needed. I then started JBoss and went through the errors in the log to figure out what dependencies were missing, deploy them, and then restart JBoss to get clean logs. I think I had to restart about five times to catch all of the necessary services.