NEED HELP designing a small forest garden

Hi all,
I'm trying to do something with the backyard of my building.  The building itself is 3 stories high, and borders the west and south sides of the yard.  My neighbor's house is 2 stories, and borders the east side.  To the north is a 7' wood fence.  There's lots of light, but only a few hours of sun in the morning, in the summer, when it's actually sunny.  In addition, there is a 30' cedar tree which shades the north end of the plot.  A lot of the summer is overcast (I'm right at the beach, in San Francisco).  I'm in zone 10b, Sunset zone 17.  No snow or freezing, rarely gets above 75, altho we do have some hot days.  No rain from May through October, but I can water.

I'd like to build a little forest garden around the cedar tree.  Sort of like a glade in the forest type of thing.  I'd like an open central area where I could put a bench or a chair, and sit and read or knit.  

Most of my experience is in growing food.  I've never designed an ornamental garden.  I need help in picking plants and in placing them.  I'd like it to be colorful and smell nice.  I'm thinking coleus, caladiums, begonias, astilbe, bleeding heart, ferns, flowering maple, Scotch moss, honeysuckle.  I need ideas for height, like a small, pretty tree that flowers or has pretty colors.  Japanese maple?  FLowering cherry? Maybe something that gives fall color, altho that can be dicey here, since it doesn't get cold.

I drew this sketch of the plot, with the measurements added.

Maybe a Daphne shrub. They’re pretty small and could hang out in the understory of larger plants. They don’t enjoy a lot of light and are the first plants to bloom here in February. Zone 7b. The blooms smell like Fruity Pebbles!

Scott Stiller wrote:Maybe a Daphne shrub. They’re pretty small and could hang out in the understory of larger plants. They don’t enjoy a lot of light and are the first plants to bloom here in February. Zone 7b. The blooms smell like Fruity Pebbles!

Don't know how'd they do in zone 10b, but they're poisonous and there's pets and a kid in the building.  What I really need is help laying out the garden.  I would love for someone to draw over my illustration, placing plants where they should go.  Here's a photo of the space: