I've been working on a very similar app - also based on Sönke's book. Currently everything happens in the terminal but I wanted to start on a GUI app soon. I understand that you don't intend to open source your work, but thanks for the writeup. I like the idea of going over rows and columns, I'll probably shamelessly copy that (my current version uses a tree for display, much like Reddit or Hacker news comments, but that becomes difficult to parse after some time.