When performing ring support hold, should I concentrate on having my shoulder blades retracted/clenched, and my chest forward, or is it fine if my shoulders are protracted?
Keep the shoulders neutral and depressed as much as possible. Neither protract nor retract the scapula too much.
The main purpose of the ring support hold is to develop strength and stability in the shoulders in a balanced way, to build the foundation for progressions on the rings (eg. dips, L-sit etc). For this reason it is best not to exaggerate neither protraction, nor retraction.