You can switch Scrivenings view on/off for “container documents” just as you can for folders – using the leftmost button on the tripartite View mode lozenge on the toolbar. The only difference in treatment between the folder and container docs is that Scriv’s view defaults to text-content view rather than scrivenings view with container documents. (A container document is just a doc which has other subdocs/subfolders under it in the Binder hierarchy.)
If you have typed textual content into the body of a folder item and want it to show up in compile, you need to adjust your Compile settings to make that happen. You would specify that for folders of that section type, their Text content should be compiled.
You can change the behaviour if you prefer, so that clicking on text groups also uses Scrivenings (or Corkboard, etc.). The setting is in the Behaviors: Folders & Files preference pane, with Treat all documents with subdocuments as folders.
As for having your folders print both a heading and their text content, you don’t have to roll you own, as most of our built-in compile Formats come with alternative layouts that combine both in one. They are typically aimed at those who do not need grouped arrangements and just write short chapter-length files----but they work equally well for introductions and such. For example, if you go into Compile, select one of the pre-fabs in the left sidebar, like Manuscript (Times), and click the Assign Section Layouts... button. Chances are your folders are already using their own Section Type, listed on the left. Select that and then scroll through the available layouts to pick one. The “Chapter” layout, for example, probably does what you want.