That's a cool project. I appreciate the concept of typing with a typewriter, which serves as input only. Your description of 'maintaining the flow' is very accurate.
With computers it seems that using 'notepad' (in Windows, for example) to type ideas quickly is the closest to using a typewriter, and avoiding distractions. Just get ideas diem as fast as possible.
I wonder what would be involved in making that all work with a classic old electric typewriter, for instance the gigantic Selectric. It was a wonderfully clunky machine. You could really type with emotion!
(Ps- on the other hand, I remember a long time ago, dreaming of getting a computer so that I could type ideas; articles, projects, papers, books.)