1) problem stems from all (?) the MDBs being concurrently instantiated - after a very short time connections in the db connection pool run out (hardly suprising). Clearly I need to throttle the number of instances of this kind of bean that get instantiated. COuld also increase the number of DB connections available (definitely), but must constrain the number of MDB's because otherwise this will fail under load.
1) getting there. looks like settimg the <max-pool-size> should do the trick (probably in my service.xml file?). Not sure that I understand the help (?) file: jboss-ds_1_0.dtd which i think is supposed to explain everything...
2) A program "Hermes" may help with this part of the problem.
Within jmx-console, find your queue, and then hit the removeAllMessages button.