For laying out curves a camera tripod can be helpful:
The blue tape marks tripod foot placement for other curve centers
<--Laying out easement. As long as you are using flex track think about incorporating a spiral easement.
Spiral easement instructions are on the NMRA website's recommended standards and practices under spiral easements. I not sure but it may be S-8??
Below are what spiral easements can look like. A nice gentle entrance to a curve, gradually tightening up to the final radius. The tight curve of the underpass curve demonstrates the gradual spiral easement entrance and exit of a curve.
Because the total amount of curvature is somewhat small the upper grade primarily is formed by mainly just the easement. There is only about30" of fixed radius in the upper right of way.