I really like the subject of your painting. There's a couple of things I think are worthwhile to mention:
In terms of composition, I think there's a bit to much focus on the left side. Basically everything points to the left side (character orientation, vanishing lines and even the airship all flow from lef to right). Something on the left that guides the eye back into the painting would be nice. As is the right side feels a bit empty, although it will get much better once you've drawn the airship.
Make sure that the airship reads in terms of value, because right now it just gets lost in the background. I believe that you probably intended to work on those as you started working on the airship, but usually it makes sense to make sure the overall values are correct before adding any details to the scene. Otherwise it's hard to judge if the composition works.
Another thing that might be cool to add and might help fill some of that blank space are to make some of the ropes that attach the ship to the balloon visible.
The characters design is very nice. The only thing that bothers me a bit is the silhouette of the clothing. There are a lot of folds but the silhouette is quite flat.
I am really excited for the finished version, this painting sparks so many cool ideas.