There is no need for OSGi-specific interfaces. Review The Book bean interface section.
2
b
Having configured the project packaging, maven-bundle-plugin, and the distributionManagement in the project POM, Maven will deploy the bundle and update the repository descriptor when you include the deploy target.
3
b
Implementing a BundleActivator (and declaring it in the bundle manifest) will give you access to the BundleContext during the start and stop of the bundle. The context can be used to register a service.