Well you already have some towns it seems. It's pretty good.
People will settle on plains where that can make their crops grow. Cities will develop along trade road that depend on the geography. Road passes near water sources for example.

If you want an historic powerful city take Vienna as an example. It is in the middle of Europe but sits at the intersection of 2 trade roads. East-west on the Danube and north-south linking the Adriatic sea to Northern Europe. Plus, it is located in fertile plains. Constantinople is another example that come in mind.

So the population don't just settle near the coast but inland as well. As long as there is water and fertile lands people can live ther but important cities develop alongs trade road.

And like you said people go where they can make a profit, so trading cities tend to attract more people, thus making them more attractive for traders.