I would use something on the line of fine or medium cinders. Whisker tracks wouldn’t ride on bed of ballast. Seeing you bought a Ross turntable. Hopefully you will be using Ross track around it. With the Ross track especially if it’s weathered. It just sits on top of the ties like the prototype. No web to hide. You really don’t need to heavily ballast the track. A good texture using cinders will look fine. Some weed tufts to break up the all black look. A few between the ties to.
