I would ( did ) start with a fan-filled circle 64 vertices and extruded and scaled to get the outer depth, then worked into the center…the 12 openings were created with another empty circle and a curve and array modifier…once in place…went to orthographic view and used the array and knife project to cut the arches…hide the cut-outs and used another circle to cut off the ends… then separated the ring section and added a solidify modifier…