Planning started the old-fashioned way, with pencil and paper.
I worked on squared paper, planning routes up and down through five layers. I exploited the squares' size to plan 20mm channels, allowing both one cent
and one penny
coins to be used in the maze.
I then scanned the sketches into PDF files, and used InkScape to "draw over" the PDFs, and save the digital versions as DXF files.