I have some insight in this as I'm currently building a very similar project myself. I'm using off-the-shelf components and the relatively cheap USB driver boar

I have some insight in this as I'm currently building a very similar project myself. I'm using off-the-shelf components and the relatively cheap USB driver board for the 10.3" ePaper display is more than capable enough of showing a variety of content. Typing in a document or code is plenty fast, scrolling a webpage is usable, but you'd probably want to use PgUp/PgDown, moving the mouse around is fine but I'm using a tiling window manager to avoid having to drag windows around. I'm able to drive video, but it's quite choppy. In general small updates are plenty fast (like showing characters next to a cursor) and big updates are slow (like full screen video playback). Playing video in a small window is fine if you just want to get some information out of it. All these speeds are in a dithered 1-bit mode though. As soon as you start playing around with grayscale things starts going slow (you essentially need to display N levels of grayscale as N frames). The system I'm using is capable of updating parts of the display in 1-bit mode and others in "high-fidelity" 16 levels mode. This means that I could e.g. tell it that my picture viewing program should use the full quality mode, and my text editor should use the fast mode. Since I'm using a tiling window manager opening a picture would then use about a second to display the image, but once it's there I could type into a window next to it at full speed. It could also allow me to highlight areas to redraw in high-quality mode if I was browsing a website for example and wanted to watch a particular image.