How should I be planning my reduction print designs?
If the have a computer drawing program such as Photoshop, gimp or Inkscape you could use those programs layering ability to simulate the different cut and colour "layers" you are looking to achieve.

Each layer would correspond to a cut and color.

Different pen tools could also be used to simulate different cutting tools.

And the zoom feature would allow you to assess the graphic presentation and design quality at various scales. Software scale able thumbnail feature.