I really like the idea of having a significant chunk (a whole film) with Din and Grogu apart. It adds more weight to the relationship, and I think the storyboard you’ve presented leans into that well. I’d absolutely like to see a Book 5 as you’ve proposed.
I must admit I’ve always found the order and motivation of events a little confusing between MandoS2/BoBF/MandoS3, but you writing it out like that makes it abundantly clear just how haphazard it is. Anything that cleans that up is a win in my opinion because the moment to moment content is still great.