Generally the approach is to present one idea per academic paper. You have one basic hypothesis, and one method to test it. If you have more methods to try, you present those experiments in other papers. If you have more hypotheses, you test them in other papers.
In the natural sciences you usually find that a research team publishes a string of papers on the same research topic (e.g. time perception). In literary studies you can both find a scholar testing the applicability of one method (e.g. feminist reading) to a wide variety of texts, as well as a scholar applying a variety of methods to one text or corpus (e.g. a specific author or literary epoch or even an outstanding single work).
A monograph can then be a collection of all results that you and/or your fellow researchers found. The theme of the monograph can be defined by a methodology, a genre, an author, an epoch, etc., or a combination of these.
Scientific progress is cumulative. No one expects one scholar to fathom the complete width and breadth of one topic.
In my time, the criterion for the success of a scholarly dissertation was that it had to present new insights and contribute something new to its field. The best way to learn about the scope of a dissertation, is to read other dissertations, ideally from the same field you work in. The closer their topic and methodology to your own, the better. And read the original dissertations, not the re-written versions published as books.