Big work! In the end, the Form is Theme and Variations. As I thought it is not easy to go out of that field.
Anyway, this Form is good to make a variety of developments, which I thing you fulfill quite well. When one listens to the thole piece, there is also a sensation of climax with variation 10. The one in pentatonic scale sounds a bit out of the general style. But the inner development of each variation is rich. The fact you chose the tonalities step by step is a rightful method, however modulations are sudden and abrupt. Some sort of transition between parts would have been perfect.
Regarding orchestration, you make better use of the strings. The piano seems to stay back particularly in long chordal passages, or when it doubles the violin or the cello. On the other hands, some times the piano is fully independent (variation 9). I don't know if the quadruple stops and so are possible, I hope... But a recurrent issue is the expression slurs in the strings (to write it or not?).
The score is clean and everything in its place. Some high lines of the cello should have a change of key signature. The audio is good.
The theme is recognizable in the variations and it plays a "glue" role.
Congratulations!