I'm happy with the output right now. I thought the right-hand motor was slipping / behaving inconsistently, but I've re-done the GPIO connections and I think one of those may have been loose previously. One thing I don't yet have fully worked out is the dimensions of the drawings - I've tried resizing in Inkscape, and also providing a larger plot area to the gcodeplot Python program used to convert to gcode, but I'm still not achieving the sizes I'd like.

As mentioned in a previous update, I've now trimmed the board down to 60cm x 60 cm in size and I'm nearly ready to put it up on the wall.

I designed a new holder for the circuit and motor driver boards, but the first print was a bit too tight so I'll add a few mm and reprint shortly. I also made a couple of small printed "feet" for the bottom of the board so that it will stand slightly tilted away from the wall at the bottom and give the pen a better surface to drop onto.

From here, I'll also need a fairly lengthy USB cable (at first) since the process to plot is still direct gcode commands over serial. Once the upcoming art show is over, I'll look into ways to have this work over WiFi, to take advantage of the Pico W. 

One final thing I'd like to do is to set up a way to record the plot process... will have to figure out an appropriate way to mount and point a camera at the whole setup!