I am interested in creating a plugin that when installed will add a custom Item Type to an Omeka install. Has this been done before? If not, does it seem doable and would a plugin be the best route? If so, any ideas on how to get started?
This is definitely doable, and would indeed be a plugin. If it is just for a single site, it might be quicker and easier to add what you need via the admin interface, though. Otherwise, the plugin would use the install hook to insert the necessary data.