Lagrange is FAST. Really, really fast. Lots of Cat3-pros. They definitely will not wait up. Not one second. I love the Sunday LaGrange ride, but you really have to pound to have any chance of keeping up with even the rearmost riders.
For other rides, the best place to go (by far) is the intersection of Ocean Ave & San Vicente right by the beach. Just get there around 8AM and there will be loads of various groups, from 2-person groups to 5+ person groups of all different abilities doing rides. Just be nice, ask, and join if welcome.
Just be aware that they'll likely be doing their own thing, and they might not want to wait up if you flat, etc. Still, it's way better than riding solo on PCH. A good thing to do is to join a group until you get to a climb that you want to do off PCH - most groups, even fast ones, ride mellow on PCH for safety reasons, and then hammer on the climbs off PCH.