Patching and Plastering - How to attach foam trim to a stucco column

We've had some garden concrete block walls and columns installed by a licensed contractor. We are hoping to stucco the walls ourselves. I'd like to trim the columns to match those around our house. I know they used foam when our house was built. Can anyone tell me how to attach the foam trim? Does it go over the brown coat before the color coat? Should we put fiberglass mesh over it for strength? Also, where can we buy the foam? I live in Northern California, by San Francisco. Another question, is there a special way to shape a rounded cap on top of the column? or, is it just done visually?
Thanks for any information or help.