Let's face it this could still change but here is the final idea.
Last time I build a harbour style layout I used the Scalescenes Dock Edge. I reckon that I'll use the same this time. It's easy to use. Print it off, spray it with matte varnish (I use Micador), cut it glue it and attach it to the dock wall. I used wood for the pylons instead of the paper ones which come with the kit. The dock edge also comes with cobblestone or concrete top for your dock surface. I'm a sucker for cobblestone.
A couple of nights ago I inserted some polystyrene foam around the marina area and where the ferry pontoon will be. I covered this with some polyfilla that I had. It probably isn't ideal but it would have gone off before I used it again. The next step,which hopefully will be this weekend, will be to spray the plaster with acrylic wash and when that has dried paint in the water colour. I'm planning a green to match the algae on the bottom of the dock edge.
Hopefully it will all go well.