I recommend using a custom settings.xml file to define the staging repository. The custom settings can also point to a local repository that is specific to the test build you are running. This will ensure that you don't pollute the system-wide local Maven repo, and ensure that you are testing from a clean repo.
You can use the specific staging repo URL in your settings.xml, or you can use a group URL which includes all the staging repos:
Regarding the nexus maven plugin, you can use that if you like. There is documentation on the sonatype site: