I would put one on each side. Now that I know your location I think you should cross post to the California Gardening forum. You could also plant Vitex or Chilopsis. You will get more responses from Cali gardeners there. The California forum

Here is an article from the LA Times about a yard done by Gabriela Yariv for a Greene & Greene home in Pasadena:

http://www.latimes.com/home/la-hm-pippert3-2009oct03-story.html

To gain graduated heights in the front yard, Yariv used a Bloodgood Maple (as you are considering), Gingko, and Arbutus 'Marina" (Strawberry Trees). You likely do not have the depth in your yard for the Gingko, but you do for the Bloodgood and the Arbutus (perhaps Arbutus unedo 'Compacta,' the dwarf strawberry tree).

As I understand you, your house faces east, so the taller of the houses on either side of you is to the north. If I were you, I'd curve the edges of the lawn toward the pathways at the inside corners and toward the outer wall at the outside corners to create larger planting areas for the trees. Then, in the open area created by the curve at the northeastern outer corner, I'd install three Arbutus unedo 'Compacta' in a loose triangle to frame the house and yard from the street on that side (without blocking the window). Then, in the open area created by the curve at the outer southeastern corner, I'd install the taller Bloodgood maple to frame the house on that other side. You might also consider installing one more Arbutus unedo 'Compacta' on the southern side in the open area created by the curve of the lawn toward the interior pathway leading around that side of the house.

Forgot to mention: Beautiful home! And, I love your existing garden areas. The stonework is lovely and adds a sense of permanence. Will you be adding stone to the bare wall at the sidewalk, or something to climb that wall (or drape over it)?

Although I love Blood Goods, I feel like its brick color (in full sun) will blend in too much with the darkish siding on your home. Likewise, although I love arbutus (strawberry trees) their foliage is quite dark green and the gorgeous trunk is very dark red which will also blend in with your siding.

If you like those trees I would pull them out to the front of the lot rather than being closer to the house. Another possible option would be the coral bark maple (don't remember Latin name) which has bright red/crimson trunk with lime-colored foliage. Both of those colors would provide more contrast with the house.

I think the house needs a less contrasting trim colour, perhaps a cream or warmer white, then perhaps a pergola or gate at the street side. Lots of good advice about planting above.