I am sure there is something wrong in your etherpad installation. The "editOnly" Option should be true. This option prevents creating new pads over the web interface. The creating of new pads over the API is still possible.
I don't really understand the last question. In Moodle you can create multiple instances of the Etherpad activity. Each instance has its own pad. The name you define in the plugin configuration is only a suffix of a group pad. A pad build by the API should be named like "g.jfldjflsfjlfs$moodlepad" (moodlepad is the part from your configuration). You can look at your iframe src url to check this. It should look like: