I'm in the process of creating some custom components. The information on the Avoka Support forum seems to be very basic. A document on what the widget.json schema looks like would go a long way in helping understand what the scope of possibilities are. For instance:
Take a look at Maestro Native Component Toolkit ... it has templates that will show you most of what you want to do. The templates are designed to include features that you delete if you don't want them.