I've done something similar.
my advice:
Start with the most detailed topo map you can find.
Better yet, the site plan for the property.
maybe available from the county.
you may or may not want the track to be level.
buy 200 little survey flags from a hardware store (they are attached to thin metal wires that you can stick into the ground easily) and stake out a tentative route.
buy a metric measuring wheel (about $100 or so).
look on-line for the standard curvature of a 400m IAAF track.
you need not match it but you don't want overly tight turns.
start a blog of this project.
rodger