From a warm weathered California girl to a warm weathered Miami girl--it will be too cold for the beach (assuming you mean water touching your legs), unless there is an unseasonably warm spell. I was there the first week of April this year for an agility trial, and wore a hoody the whole time. All the same, bring warm coats, walk along the sand, and enjoy the quiet of the off season! I'd stay in a hotel right on the water, since rates should be cheap that time of year!
There are several beaches in the area that are dog-friendly in the off season, so Merlin should get a nice romp in if you want to go that route