Hang the retroreflective fabric using spring clamps, magnets, or even gaffer's tape. You will want it to be very close to the subject for best performance. This helps to avoid a halo effect.
Light Ring Mount
Mount the ring light on your camera, then power it via the USB-C port on the QT Py.
In this shot I've got an LCD monitor showing me what the camera sees -- this is a great way to see how the greenscreen looks, since you can't see the effect with your naked eye unless you're positioned right behind the camera.
Here's a behind the scenes video of the system in action: