Welcome to the forum!
Before importing the camera, I would export the terrain from Max as an OBJ (or a proxy of your terrain). Bring the OBJ into Terragen and make sure it has the correct size in world space (Terragen units are metres). If the scale is off, then usually it's by a factor of 0.01, 0.1, 10 or 100.
Now see if the camera sits correctly in this space. If not, it's usually just a scaling issue, as with OBJ, so try reimporting with different scale factors.
Rotation order shouldn't be a problem with FBX.