Hi Dave:
I think you are getting good input for waterproofing.
Maybe you are already aware, but there could be significant scouring from waves on a beach front retaining wall. It could cause the wall to be undermined. I see many examples of this on our Southern California beaches.
The owners for beach-front projects we have done hired a consultant to evaluate scouring, among other things, and make recommendations. Another option for perhaps a small project or a short retaining wall could be to visit the building official in the City and review recent projects in the same beach area. Deepened footings or caissons are common.
Respectfully,
Bob Freeman, AIA, EIT
Integrated Design Services, Inc.
(949) 387-8500