I would make the end of the garden larger on the left side to accomidate either a crape mertle, queen palm, olive tree, etc. The front area of the walk on the left side should have color flowers (annuals), as should the inside right corner, and maybe space them up the walk also. Fill in with some hawthorns and some other hedges that can be groomed into ball shaped (I think we have holly bushes). I would use the holly bushes up the walk as the are small in overall size (18x18). Hawthorns get bigger. All that stuff is relatively inexpensive, easy to trim and up keep.
Maybe a little color on front of the window on the left side with some hawthorn, or hedge.
I would stick with 3 types of plants (non annuals), one or two types of annual color and then the one tree. Assuming almost all areas get lots of sun.