Answer: For the sunny area you might try the soft mounds of mugo pine or yew ( yew does not have to be clipped into formal shapes, after all) or possibly some of the mid sized junipers.
Unfortunately, maple trees are difficult to underplant successfully because they are so greedy for nutrients and water in addition to blocking sunlight and rain from reaching the ground. The shallow roots of pieris and rhododendrons would not, in my experience, be able to compete successfully with a maple because they need an evenly moist yet well drained soil. For this area you might instead consider some fencing with a vine such as fall blooming clematis or English ivy fronted by some large containers of annuals.
Have fun with your project!
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