What data are you exporting from Gaea? I tend to use the Mesher node and at its default, it produces a very dense mesh.
Plug your final texture map into the Color of the Principled BDSD node. Set the Metal value to zero and the Roughness value to 1, unless there are specific reasons you have not to.
If you export any data maps, such a flow, height, slope, use those in the Node graph as you would any masking input.
Is there something more specific that you are looking for?