Shoreline model

Hi to veryone.
I’ve been asked to realize a 3D view of an ancient historical site near the shoreline.
I’m not scared about the modelization of the ruins, but I think it will be difficult to realize a good model of the shoreline.
Hereinafter some pics of the plastic model I shall use as a reference (I apologize for the poor quality of the pics).

I’ve been asked to respect the altimetry and the general topology of the region.

I would like to have some advices about the logic to be followed to model the shoreline.
At first I thought to use Terragen 2, I tried it and I found it quite good, but as far as I know you can’t control or initialize it by means of heightmaps (feel free to correct me if I’m wrong). Since I have to respect the topology, I discared it. So I think i shall go with heightmaps.

I’ ve many doubts about the way to proceed: shall I use heightmaps and create a mesh by myself (displacing the edges in order to follow the altimetry lines) or it’s better to create a greay scale map to be used as a displace map?

Concerning the ondulations of the ground and the rocky coast, shall I create them by using a bump/displace map or it’s better to sculpt them?

Shall I create a unique huge hi-res mesh going from the sea up to the far hills or it’s better to create separate meshes (rocks, crag, hills) and manage their interfaces?

What’s the best way to proceed, taking also into account UV mapping and texturing phases that will follow?
How would you do the job?

Thanks in advance!