This page covers a few additional parts I found and things I learned which I didn't use directly but could have in some variation of the designs.
First, the M3 nylon screws and standoff kit was so useful that I did some searching on DigiKey for similar M3 parts and found these:
On the right are the 6mm and 12mm standoffs from the kit Adafruit sells. On the left I'm showing examples of similar black nylon 6mm, 8mm and 10mm spacers that I found on DigiKey.
These parts are fairly expensive to buy in small quantities, but if you need them, you need them!
A similar thing I also found at DigiKey is these M3 standoffs with screw parts at both ends, shown below.
I looked at several additional pairings of matrix panels and art canvases. Some of these will work great and others didn't pan out.
First, the 32x32 pixel panel with 6mm pitch shown below measures 190.5x190.5mm. The 64x64 panel with the 3mm pitch used in the third build of this guide is just a tiny bit larger, at 192x192mm. This means the 10x10 inch low profile canvases will work great with this 32x32 pixel panel.
Continuing with the above idea, but scaling down a notch, the 2.5mm pitch 64x64 pixel panel is 160x160mm. That's exactly the same as this 5mm pitch 32x32 pixel panel.
I would really like to find a frame thinner than 10x10 inch for the 160x160mm panels.
I tried 2 variations of 8x8 inch canvases. They are described as essentially the same, but the 2-piece "value pack" includes canvases with thinner framing than the single canvas.
Unfortunately, this pairing did not work. It may be hard to see in the pictures here, but the 160x160mm panels are about 4-6mm too large to fit inside even the multi-pack 8x8 inch canvases.
However, the 8x8 inch canvases could be used with the smallest 32x32 pixel matrix, with 4mm pitch.
The 8x8 inch canvases have about 6x6 inch of interior to work with. The panel above is 5x5 inch (128x128mm), so it will fit.
Finally, I looked at one additional possible pairing: a 6x11 inch low-profile canvas for the 3mm pitch 64x32 pixel panel (used in the second build of this guide).
Unfortunately, this won't work because the panel is 7.5x3.8 inches, but there is only about 3.3 inches of interior space in the second dimension, so it won't fit.
The Matrix Portal has a STEMMA-QT port, a JST 3-pin header and several GPIO breakouts, so there are a lot of possibilities for adding extra magic into (or on the front of) your canvas.
In the picture below I'm mocking up an idea where I will string a flexible RGBW LED strip around the inside of a 10x10 inch (low-profile, multi-pack) canvas and place one of the 160x160mm matrix panels in the middle.
I'm using a JST adapter cable to connect the Matrix Portal to the flexible LED strip. These parts are shown below:
Update: The arrangement above did not work. The NeoPixel strip acts very flakey, in a way that suggests there isn't enough power going through the JST connection.
I tried something else using the same parts. As shown below, I cut the red and black wires on the JST adapter, near the header. Then I stripped the red and black wires and connected the red wire to the 5V screw terminal and the black wire to the GND screw terminal.
This solved the power issue. There is still an issue where the matrix panel LEDs flicker when the NeoPixel strip is being updated. I'm not sure how to fix that, but otherwise it looks really good!
There are lots and lots of other "flair" possibilities, especially with the STEMMA-QT port. Another thing I'd like to try is placing one (or both) of these ranging sensors on the front of the canvas, and then use them to detect presence of someone in front of the canvas.
... I could keep on going with flair ideas, but I think it's time to end this guide. If you're interested in more projects with wall hanging computers on canvas, using a Raspberry Pi for the system controller, check out this other guide I wrote on the topic.