When using existing or new hardware, an important point that often gets overlooked is the space or amount of room needed for the installation of window treatments (drapery, roller shades, valances, cornice box, etc). For example, you need to know how much room you will need between your blackout and sheer drape. Or if you have a roller shade and a sheer drape, etc.
To keep it simple, you should always consider 3 inches of space between your window treatments (including the wall). If you have a valance/cornice box, a blackout drape, and a sheer they should all have 3" of space between on another to avoid the drapes from not traversing smoothly.
A great tool to ensure the best spacing when ordering drapery is to ask for the dual drapery rod where both tracks come in one piece.