Should there be one component for each piece? Yes. To get a good parts list, treat each piece of wood as a component. You can create just one stile and one rail then use copy/paste, mirror or pattern as needed.
How do you group the components? Create a new component and drag the member components into it. That creates an sub-assembly under the active component. I suggest you do that only under the top level to keep things sane.
Should they stand alone? should they be sub components under a master component? Should they be grouped together under a an assembly? Use the semantics of the cabinet as a guide. A base cabinet has a carcase, (optional) face frame, (optional) drawers, (optional) doors, and (optional) shelves. Other than shelves and sometimes doors, those main parts are assemblies or, more accurately sub-assemblies thus their components would be in a container component.
