based on dsf.commands.basecommands.evaluate_expression. Since RRF expressions aren't automatically resolved as they are intercepted you have to do it yourself.
I have the same display. Its very nice. But it definitely needs a case or at least a good back cover. It's on my list to make. But if someone here beats me to it or finds one in the wild. Post a link.
Are there any problems/concerns with powering the Duet and the RPi from a 5V PSU? Is that overkill? Although with the addition of a bunch of Neopixels it might be necessary.
Nothing wrong with that at all. In fact it allows you to use a relay to control the main PSU on and off.