do I need an JBoss specific deployment descriptor for the resource adapter?
No, as your resource adapter is pure inflow you won't need that. Once you add a connection factory or an admin object you will need to add an ironjacamar.xml or define a <resource-adapter> entry in the subsystem.
do I have to modify the standalone-preview.xml also for an inbound resource adapter?
No, same as above.
do I need something like the @ResourceAdapter annotation in my MDB?
Yes, you will need to point it towards your deployment.
if my inbound resource adapter is correct, should I see it in the management console under "Connector" -> "Resource Adapters"?
That is a TODO.
If you don't deploy as an .ear file you will need to link the two deployments together using a META-INF/MANFEST.MF entry - see http://community.jboss.org/thread/169894 - like
Dependencies: deployment.RA_UDP.rar
inside your .jar file.