I think that you are on the right track in honing the comparison between Trotsky and Stalin with Snowball and Napoleon. In contrasting them, I think that part of your analysis can be focused on how Snowball is more along the lines of the revolutionary figure, while Stalin embraced the revolution but recognized the exercise of power as fundamentally more important. Orwell certainly sees this distinction. Snowball is the more clever, quicker, and more skilled one at public speaking. Orwell describes Snowball as enjoying talking with anyone at any time about the revolution and its force of change. Certainly, Napoleon is as much committed to the revolution, yet afterwards, it becomes evident that he is more concerned with the idea of his own power and doing whatever is needed to safeguard it. The taking of the puppies early on is an example of this. While Snowball is out making committees and doing his best to make sure that the tenets of Animalism are embodied in the post- Jones world, I think that Orwell establishes that Napoleon is more concerned with establishing the base of his own power. With this contrast, Orwell is able to make Squealer more like Trotsky, who was more driven with the revolutionary element. At the same time, he is also able to make Stalin's tendencies for control, brutality, and the elimination of dissent and competition needed ingredients in Napoleon's characterization. Accordingly, I think that being able to bring out such contrast in the pigs will help bring out the contrast in your analysis of the historical figures, as Orwell constructs the former with the understanding of the latter.