What a blast this has been to learn and build. Thank you to everyone who put this together and all the valuable contributions by other builders.
I went with 24" pipes, requiring a platform that was 28" square. The base is 1/4" plywood with oak side rails to provide stability and insuring a flat surface.
The legs are temporary so I can get it working and debug. I still haven’t come up with a table to install it in, but at some point I’ll have to decide what to do.
I ordered the wrong magnet and so I can’t see the ball tracing a pattern yet, but once I get the correct magnet I’ll post a video.
I have been able to get the unit to draw a simple circle and to home properly. So I feel that I just need to continue the build to the finishing point where there is a piece of furniture.