Walter,
there's no nightly build yet. For development, the easiest way is to checkout the modules to top-level projects from trunk into an Eclipse RCP installation. You can then run the plugin by right-clicking the .eclipse project and selecting Run as > Eclipse application.
That way, you can pull in updates from subversion and run your extensions against it.
To create installable update sites, the easiest way is to run mvn targets on the parent module project. That will create a local update site in the .updatesite project's target directory.