Adding metadata is not that difficult. If you press either button a pop-up should appear. In that pop-up you can select the metadata you can add. These are the only official metadata groups and roles.
Calibre metadata is only used for Calibre (and I seem to recall one reader) and nothing else. In the current metadata standard there are no equivalents for series. You can enter any type of metadata in the OPF, but don't expect anything or anybody using it or even seeing it.