Closing multiple contour lines with z-height and preparing for

I can’t figure out how to solve this: 1 I want to close all of my contour lines with different heights (z-value) (main question). 2 Lay them out on the world plane, making them ready for laser cutter, maybe numbering them - the most efficient way?

6. Measuring Height Differences - Part 2

Creating a Surface from Contour Lines using Patch Surface

Contour maps (article)

Matplotlib - 3D Contours

How to make a closed terrace terrain from contour curves - Rhino

Closed Contour - an overview

How to Create Contour Lines in QGIS

MAPS: CONTOURS, PROFILES, AND GRADIENT

Contour plot of matrix - MATLAB contour

How to Read a Topographic Map

The Shapely User Manual — Shapely 2.0.3 documentation