Surprisingly easy! I was scared of building TUI like this because it seemed so complex, but it's actually not that hard. Or at least, with tui-rs[1], which is surprisingly easy to pick up. Once you read two or three examples, you'll gain pretty good overview of how to build applications with it. I can definitely recommend it, it does all the heavy lifting and leaves surprisingly little for you to care about. Just don't forget to unset terminal raw mode before your application exits, or else you'll start breaking people's terminals :-)
[1]: https://github.com/fdehau/tui-rs