Thanks for the report. You can avoid the stretch of PCH from Entrada to Temescal Cyn going North/West if you cut over to the beach bike path. You can either take Ocean Park Blvd all the way to the bike path (south of the pier), the California Incline overpass (north of the pier), or the tunnel under PCH at Entrada (you'll need to exit through the left-hand exit on the other side of the tunnel and carry your bike up some stairs. On the way home, you can get off PCH and cut through the beach parking lot even before you get back to Temescal -- almost at Sunset.
Also, you may want to cut up to San Vicente to take you over toward the coast. It's nicer and a major route for cyclists to get most of the canyon rides in Brentwood or to the coast.
I agree that Topanga is also fairly busy. If you take Topanga again and don't mind more climbing, take a left at Fernwood and climb all the way up to Saddle Peak (about a 2400' climb)
If you decide to climb Latigo, you'll probably want to drive out to Malibu to start there unless you have a lot more time. A ride from Santa Monica that includes Latigo is about 65-70 miles minimum.