To get more control when rotating with the mouse, there are two techniques.
First, position the mouse pointer far away from the center of rotation. The closer the mouse is to the center, the greater the rotation for tiny mouse moves. The further away, the more you have to move the mouse to get the same amount of rotation.
Second, holding down the Shift key while dragging the mouse turns on “fine tuning” which cuts the rotation down by a factor of something like 10 times, so you get a LOT of fine control.
You can see the normals by turning on either vertex or face normals in the mesh display panel of the n-tool shelf (in edit mode), but that will show all the normals, not just normals for a single face or vertex. With a terrain model, that will probably look like a crazy pincushion.
You might pick a representative face on the model, and extrude it along its normal, to get something visible to use to orient the mesh, then delete the extrusion when you’re done.