Richard, Love the photos, and we can see what you are trying to achieve. You now have your blueprint and there is no reason to be afraid of starting your project. Study the shapes of the Island of moss and the outer edge of the gravel in the photo. Pay attention to the shapes you see, lay out your edges with a hose or something similar and decide how that should take shape before starting. I like the idea of having the outer edge raised slightly and a good use for the sod you remove, I am just not sure about drainage. If elevated too much it may make a mess of your raked gravel area. Study stone placements and research that before placing your boulders in your raked gravel area. I think you are well on your way to a beautiful garden.
The photo's of how you would like to see your maples look is very similar to one of our members gardens. I hope he recognizes the similarities and gives advice on how he achieved his beautiful woodland garden. What planting Zone are you in?