I'm using one of those devices with a tiny eink screen... as a pocket ebook reader. Sorry for the bait. Fun and easy project though, lookup Pala one if you're interested and dm me for improved firmware (restrictive license)
BW. I don't think colour would do much, as the screen is 250x122. Battery may depend on what you can find, but the one I have should last several weeks (still testing). I started on a tiny LiPo I ripped from my cat's floppy fish toy.
To give more info here, it uses Heltec Wireless Paper, which is a self-contained unit and just needs a battery added.
Would be great if it also ran some type of Topo mapping software!