I like to use 7/16″ for quarters and 1/2″ to 9/16″ for halves. For dollars, i use 5/8″ to 3/4″. Pending ring size and overall look. Larger holes mean narrower band width. The hole size doesn’t effect the ring size as the size can be changed. You will need wider bands for larger rings as they narrow as their stretched. Smaller rings require larger holes because the bands widen as they are reduced.
Good idea to start there. Clad quarters, clad halves and clad dollars then into silver coins, gold and platinum.