congratulations! nice start!
here is a screenshot of the available blocks
you might want to add an icon for the extension like this
Extension icons: Until now, icons needed to be compiled as part of the MIT App Inventor build or hosted externally using an HTTP or HTTPS URL. Now it is possible to include icons in the extension. To do so, create a directory aiwebres in the same package as the extension. Add a PNG file for the icon, and name it in the iconName field of the @DesignerComponent annotation, for example “aiwebres/icon.png”. When the extension is packaged it will be pulled into the AIX and the SimplePaletteItem will correctly load the icon from the MIT App Inventor server.
(taken from https://groups.google.com/d/msg/app-inventor-open-source-dev/aSQda5uR-1k/sUcuiy6zAwAJ)
the icon should be 16x16px