What does the purpose for the windmill was used show about the pigs priorities? Explain whether their priorities are consistent with the aims of the rebellion?

No, the pigs main stated purpose for the rebellion were based on principles (evident in the Commandments). Telling the animals their main priority was to build the windmill was based on the new "economic principles," embraced by the pigs (the leaders) and fulfilled by taking advantage of the rest of the animals.