1 / notification.verbosity is not documented. Here is a blurb you can copy paste :

notification.verbosity Int, Define the verbosity of notifications, use 3 to spam your channel to death (everything is notified) up to 0 for less notifications (only tasks related)

2 / According to the doc, the channel(s) to join should be read from $this->getConfig('notification.channels'); and not from $this->getConfig('join');