What a lovely shade garden you are going to have. The stepping stone idea is excellent. First layer 8 to 12 inches of compost and two way mix on top of the lawn and moss. Two way mix is sand loam used to start lawn. You may want to use gravel beneath the stepping stones to keep them stable. I suggest a gold and black tapestry garden. Use lamium \'Golden Anniversary or lamium \'Aurea\' as the main groundcover with black mondo grass poking out in clumps near the stepping stones. Primroses, especially the candelabra primroses will thrive here as well as the dark foliage of Japanese painted fern and Heuchera with dark leaves. These evergreens will look great in the winter months. For summer color add several large pots sitting on flat spots in the design and fill these with potting soil. An evergreen \"Golden\" yew in each pot will give it year long form and color and surround the main evergreen plant with shade loving annuals such as begonias, impatiens and lobelia. The only summer flowering perennial that may bloom here is the somewhat invasive Japanese anemone. There are some dwarf forms of this perennial. By limiting the color palette and grouping plants together you will create a calm but beautiful space. Send us a photo when you are done and don\'t fret if you come up with better ideas as you dig in. Gardening is all about experimenting. Keep growing, Marianne Binetti