First, the E Ink devices do not scroll they page turn. They need to create the full page and don't move pixel by pixel.
Second, a eBook Reader has a 4:3 screen so it holds more data than you might expect when compared to a typical smart phone. See
screen sizes in our wiki to figure out what size screen you might need. You can use the dimensions given on the page to cut out a piece of paper the correct size. Cutting a news paper can give you an idea of how much text you can see.
Generally an android device eats batteries due to wifi and background processes. If you manage this it can do ok on battery life.
E Ink screens create the image and no power is used to maintain the image unless the
front light is on. See our wiki for how this works. For background you might want to look a the
Category:EBook_fundamentals for a selection of basic eBook data.
Good luck on your quest.
Dale