Researchers and editors are often over-focused on their topics of research. Well, that is expected. But, any publishing including on-line publishing is much more than topic one researcher deals with. The publishing consists of many technical, social, legal, communication and scientific aspects. Communicating science is much more challenging and complex activity.
The Open Journal Systems that you will probably use for the publishing of your journal will provide you with means and tools to communicate your journal to the public. But, the system itself is fully meaningful if you use it properly and wisely. Entering metadata properly will support meaningful, informative and educational search that will help the students, people from different disciplines, journalists, policy makers. Do not surrender to consequences of overwhelming duties and tasks.  Do not think that metadata is just another boring task that should be done in a fast routine.    Read carefully, Dublin core specification and develop your way how to use it effectively in your OJS.  Disciplines, subjects, coverage can be used wisely in order to attract your future readers, authors, reviewers and other who will support you to increase presence of your journal.  On line publishing web platform is not a sort of wardrobe in which you have to put on hangers your scientific shirts/files. It is much, much more.  Do not settle with less.

Image below is screenshot from the Open Journal Systems metadata management.