Here are his suggestions for design and shape. Now I need a list of what would accomplish it in shade. Thanks for looking!
1. Gone ... or rigidly clipped into a non-overhanging, refined shape ... topiary-ish, but not fussy.
2. 12" - 18" ht. groundcover, perennial or shrub. (Dianella tasmanica 'Variegata' as one example.)
3. Something on a trellis ... like a Mandevilla ... or anything reasonable sized.
4. A colorful shrub ... like a Hydrangea.
5. Something spilling and colorful ... annuals or perennial. (The footed Victorian urn strikes me as too fussy, yet undewhelming.)
6. A bold shrub ... like the shell ginger or selloum. Or both, with the selloum behind, farther back along the side wall.
7. A cluster of small "trees" with height.
8. Low groundcover with mulch pathway through it for side yard access. Since it doesn't show, can't tell how it would really tie to the r. side of yard.

I have much the same conditions in zone 8b. Sticking to plants which require little supplemental watering, once established, holly fern, aspidistra, fatsia, and the several varieties of nandina come immediately to mind. The last has become controversial in your area, on the theory that it is "invasive." It may well be, in wetland areas, but not, I think, in typical residential environments. The theory that birds devour and spread the berries is, in my humble, urban myth. In any event, the more compact varieties, such as Harbor Dwarf, bear little, if any, fruit in shade. I've also had some success with azaleas, in large containers, but that's a tricky business.

I've tried Azaleas twice... they curl up and die within a few months. The setting sun is what I think gets them.

Many things are fatal to azaleas, including my alkaline, slow-draining soil. If you're getting that much afternoon sun, though, you might take a look at Spring Bouquet viburnum, which does very well beside my containerized azaleas. It is lovely when in bloom, but not quite as drought tolerant as the other suggestions. Should you decide to try the fatsia (one of my favorites), I would leave it in the container until you see how it reacts to the afternoon sun.

Not to play the busybody, but I wonder if your mailbox doesn't look a bit quaint against the elegant modernity of your house.

I like both the Fatsia and the Spring Bouquet Viburnum. I'll have to see where I can order it locally.
If you think the mailbox is quaint now, you should have seen what they had out there when we bought the house. A... no joke... plastic red barn. I'm not even kidding.
Any suggestions for mine? I don't want to build a cement deer-blind for it. Those just kill me. And the mailbox is in full sun from sunrise to sunset.
"Elegant modernity." I like the sound of that.
But it puts a fine point on exactly what I don't like about this house. LOL! It's too "new-ish" looking. Too tall, too loud, too much glass, too brash, too bold, too everything.

No one would be tempted to refer to your stylish abode as "cute" or "cozy" which, at least from the masculine point of view, is perhaps just as well.

Perhaps you could elicit some suggestions from 'Vark on the mailbox. He's the "go to" guy on design issues.

I would love to hire him, actually. The mailbox is the least of my worries.
I like "cute and cozy," but I think I'd prefer that my house was "simultaneously stunning and inviting."
And I think Yardvaark hit the nail on the head with his suggestions for shape and placement. Now I need plant names to pop into the picture.