Awesome project and photos, Muhammad. The plantings on the original site were beautiful, and I am very interested in the re-landscaping.
One thing I'd suggest is some kind of ground cover on the big hill above the retaining wall. I think it would help hold the hill and certainly should stop minor surface erosion on the wall and below.
In the East, there's Boston ivy, Vinca, euonymus, etc., but I have no idea what would work in CA. I was actually born in Hemet, in Riverside County, but we left for Florida when I was tiny.