When you Paste the coordinates into a Camera your current view in the 3D preview is "detached" from it and becomes a Perspective view. If you re-select the camera from the 3D Preview camera dropdown you should see the correct view.
Camera movement can be quite fast, it depends on what you are using for movement. I prefer the keyboard+mouse Alt+mouse button approach (covered in the docs). If you are using the camera movement widget in the 3D preview, the control at the bottom adjusts how fast movement is.
Finding specific coordinates can be challenging, it's true. We don't currently have lat/long available for positioning anything other than georeferenced terrain and image files. I would suggest perhaps trying to find the terrain feature you want in a real-world map/terrain view like Google Maps, then see what it looks like from an above/satellite view, and use that to look for a similar area in Terragen.
- Oshyan