EastRising/buydisplay.com has
5" capacitive multitouch panels for less than $9 USD. The active area is 109.6mm × 66.4mm, and the entire display overlay module is 115.20mm × 72.5mm. They also have different sizes of these, many with multitouch (5 or 10 points). The connector is tiny 6-pin FPC, but you can get the connector for < $0.20 USD; that way if a panel gets too scratched or whatever, you can just switch it.
A normal display would pretty quickly get image burn. Instead of a display, one could use a stiff acrylic sheet beneath the touch panel, maybe two sheets sandwiching a printout describing the tool buttons. Or something like an acrylic sheet or 3D printed support and a
2.7" e-Ink display module covering one half of a
7" touch panel. In vertical orientation, you could use the upper area with the e-ink display as buttons, and the lower area as a gesture pad (or for scrolling/panning and zooming like I'd want). Or vice versa. I don't know the exact maximum current consumption of the FT5316-based capacitive touch panel, but I understand it is of the order of about 20 mA. The e-Ink display only needs on the order of 15 mA while updating. So, this is not particularly current-hungry.
You still need an USB MCU, but I think Teensy LC/3.2/4.0 would be a good fit here, depending on what one already has available. The touch panels are standard i2c devices, with additional reset (output) and interrupt (input) pins; and the e-ink display uses a 3/4-wire SPI (with DI, DO, SCK, Data/Command, Chip Select, Reset, and Busy (input) pins).
If someone is adept at designing boards, one could use a
4.2" e-ink panel and that
5" capacitive multitouch panel with an Arduino-programmable ARM MCU, say an STM32L412 or an ATSAMD51J20 (just examples that have Arduino cores already implemented), crystal if needed for USB operation, a 5V-to-3.3V converter, and whatever voltages/support circuitry the e-ink panel needs, all on a single board with a USB 2.0 FS connector (or just pads to which to solder a scavenged USB cable). Might make an amazing DIY toolpad.