I searched around for a few minutes but didn't find anything specific. One search result that didn't specify which board was being used said that you could add up to 64KB, and there was another link where someone was experimenting with adding 8MB using some other hardware that's not intended for use with one of these devices. Which left me unsure.
From what I've read about old 8bit computers, having 64KB of RAM would make this viable and be enough for me to go ahead with trying to figure out how to make it work. Though a bit more would be nice.
My hope in the end is this can be a really compact battery powered terminal for typing. Probably look into mounting the whole thing onto a keyboard.