With regards to the commandments Old Major gives the animals, why does he see them as vices?
I think that the commandments or edicts that Old Major forbids the animals to do are the result of how he has seen humans abuse these ideas in their treatment of the animals. They represent "luxuries," to a great extent, that have been abused by humans and this reflects the disproportionate relationship with the animals. At the same time, Old Major points out these habits to avoid because animals, themselves, have not been able to partake in these, representing a level of denial between what animals do and what humans can do. For Old Major, any replication of these habits is a duplication of the abuse that humans heap on animals:
And remember also that in fighting against Man, we must not come to resemble him. Even when you have conquered him, do not adopt his vices. No animal must ever live in a house, or sleep in a bed, or wear clothes, or drink alcohol, or smoke tobacco, or touch money or engage in trade. All the habits of Man are evil.
For Old Major, human beings are seen as both a political and moral evil. The bad acts they perpetrate are abhorrent on both levels. This is why Old Major sees the habits of men as "vices," and not be duplicated. The behaviors are vices because they are the domain of human beings, a realm that is incapable of redemption and only likely to spur more vice and more sinful behavior. In this construction, Old Major has been able to give a spiritual dimension to the animals, convincing them that what they fight for is as much an issue of right and wrong as it is about power.