Re: irb .vs l3-interface

Checked deeper and looked at your config.  You have no vlans configured under

set vlans vlan-name vlan-id vlan-id

Once done, and you can call the name Default if you like, then you can add l3-interface irb.0 to the new vlan name or id

http://www.juniper.net/documentation/en_US/junos15.1/topics/task/configuration/bridging-integrated-routing-briding-interfaces-ex-series-cli-els.html