Not External EEPROM Internal Flash Memory. Semantically the same, but technically different They have an internal Boot-loader the can be accessed via the UART. Some also have the ability to self write the flash. This would allow you to store stuff there without removing a chip to put it in a programmer. Since you are mapping the Code and Xdata together it would not help to get a chip with internal XRAM.

I am not sure what tools you have, but you might want to use a separate single chip Miro to run the display and keyboard. Then connect it via RS-232 or SPI to then Main chip.

Anyway good luck on the project.