When a user saves a plan you can determine the file type it will be saved as:
Sample code
FileChooser.ExtensionFilter filter = new FileChooser.ExtensionFilter("Lesson Plan (.courselessonplan)", ".courselessonplan");
fileChooser.getExtensionFilters().add(filter);
To save the file additionally you may need the Gson package imported, which will save the lesson plan as a JSON object.
When the user loads saved file, it should be loaded to your course plan view as lesson plan of cards. There you should be able to remove cards from the loaded plan, add new cards, etc.
courseLessonPlan = CourseLessonPlan.loadCoursePlan(chosenFile);
courseLessonPlanView.addCardToLessonPlanView(eachCard, selectedLessonPaneNumber); //add to the lesson plan view