Congrats on the first image - looks like a very good tonal range there, however unintentional!
I can sympathise with trying to cut a roll film in a changing bag, when I did some similar testing last year tyring to cut a consistent length without covering the film with finger marks was a nightmare. I bit the bullet and used a whole roll at the same setting for each of the possible dev alterations. Obviously used a lot more film but made the process rther easier to manage & considering the possible benefits using an extra three or four films was worth the price, to me.
Never used the Caffenol dev but have read about it & do remember that it seemed to be a one-shot deal per film.
Have fun with the "new" set-up.