First movement finished!Below is the sketch score for the completed first movement. This duet is going to be a set of miniatures so the movements will be very short. Nevertheless, I felt the opening movement needed an introduction, which I created from the motives at A (which is also the beginning of the Diabelli sketch).
The original percussion part had timbales plus cymbal. I decided to stay with just timbales for a more consistent sound.
The overall structure for the movement is A-B-A'. The return of the opening material is modified to change its direction and point towards the final cadence.
So the next immediate step is to start working on another movement. And so I have -- the fifth.
And for comparison, the original Diabelli Project sketch: