1.  Does the Natchez Trace National Scenic Trail run the entire length of the Natchez Trace Parkway?

No, presently there are four disconnected segments of the trail that total about 65 miles of trail.  It is possible to hike the entire length of the Parkway, but it would require walking along the motor road in areas where there were no segments of the scenic trail.

2.  Is there much elevation change along the trail?

Not relative to trails you find in mountainous areas.  The Mississippi segments are relatively flat.  The Tennessee segment has the most elevation change of the four segments, but is not considered difficult.

3.  Can hikers walk sections of the original Old Natchez Trace?

Yes, portions of the scenic trail are on sections of the Old Trace.  There are signs on the trail, and designations on the trail maps that indicated where they are.