The part 3 came out and no 4 yet.
Spoilers alert!
I have a theory that if F manages to fly towards the planet, the episodes will be about meeting other numbers. Also 7 might still be a good friend to F when they will meet. Still not sure though, I am just waiting for F to later become a hero or at least one of them so letters would start to respect him and forgive him for the spelled word.
Remember this gem?
Kuma's meatriders to block so they wouldn't be writing insults under a comic that doesn't worship Kuma.