If flowering is your main goal, and you don't care whether it is evergreen or deciduous I would suggest the Chitalpa "Pink Dawn". It has the longest flowering season of any tree in my experience. It will grow to 20 feet and can be maintained there with annual pruning. It is deciduous so will be bare in the winter and of course those leaves will need raking. Roots disturbing the sidewalk is usually not a problem. Al

What about a kumquat?

Check out the newer Magnolia soulangeana cultivar 'Black Tulip', it has gorgeous deep purple-black flowers on a more narrow growing tree. It could be perfect. Magnolia stellata would also fit the spot.

'Black Tulip' is not a saucer magnolia. That's why it has a different habit. It won't be particularly drought tolerant, nor would a star magnolia. But how either would hold up through the summers would depend greatly on now retentive the soil was.

I'd visit some local public collections for tree ideas. San Francisco Botanic Garden, University of California Botanical Garden, Berkeley, University of California Botanic Garden, Davis, and so on.

Is a great place to see a collection of various small evergreen magnolias (former Michelia and Manglietia species) in pretty far along sizes. They also sell multiple kinds right there, so if a body sees one they like on the grounds they have the possibility of coming home with their own starter plant at the same time.

you may want to take a look at the Cornus Koussa dogwoods. Fruit bearing pear trees can have a not-so-pretty branching structure.

If the tree will be in a western location, a jacaranda might do very well there. The tree is utterly breathtaking when the purple blooms are open.