Curtain Hardware

Thinking whatever hardware holds the valance should be okay for whatever you want to put up. But in my experience if you don't find a stud, it's difficult to secure anything of any weight in the wallboard, even with a screw anchor.

x2 on the tension rods.

I have added some curtains in our bedroom as the day/night shades did not block enough light when we were assigned a site near a street light, or when the sun came up shining in. Therefore, I kept the day night shades and used tension rods pushed up under the valance. I can slide the curtain to one side, push up the shade and open the window if I want fresh air. Not sure about installing hardware outside the window frames on the wall. If you can find a stud, but ours is aluminum, not wood.