It occurs to me that an interesting low-power extension could be to have the device turn itself off after refreshing the display and then plug it in via a timer switch.
If the dashboard only needed hourly or daily updates and the previously rendered dashboard stays visible, there's no need to leave the Raspberry Pi running all the time.
The downside is that powering down loses the display buffer needed to correctly do partial updates, do you have to refresh the display every time - which is actually very distracting if it's sitting on your desk.
The ESP32 has the builtin capability to deep sleep and only draw a few uA of current. In addition, WaveShare offers existing micropython libraries, so it's easy to just flash an ESP32 board with micropython, get your data from an API, format it and go to sleep after displaying it. There are lots of boards with onboard LiIon management, this this setup is very easy to do.