I think that there are different ways one can go with Benjamin's insights in journal entries. The most important element to capture in these entries is that Benjamin is able to see how this story plays out while other characters cannot. He is able to see what others cannot. This does not make him prophetic as much as sad because he is unable to do anything about it.
Perhaps, the first entry could be regarding Old Major's speech to the animals. Benjamin could recount the speech and then talk about how he has "seen this before" and nothing ever really changes. Benjamin might even point to how Old Major dies at the end of his speech, almost foreshadowing that any hope in it will eventually die out. Another journal entry could be about the revolt, itself. It might be good to talk about Boxer's role in this and how Boxer is Benjamin's friend. If there is one ideal in which Benjamin believes, it would be in his friendship with Boxer. Perhaps, even some admiration might work here. The third entry might have to deal with the emerging schism between Snowball and Napoleon. Benjamin might take the position that neither of them will change anything for the animals. He might suggest that Snowball loves to talk about the revolution, but can get nothing done because everything is the work of committees. In Napoleon's case, he might talk about how Napoleon is more quiet and assuming only in his coveting of power. A nice way to end this would be to talk about how the pigs live better and require the fruit and milk mash in order to do so. Benjamin is smart and cynical enough to see the lack of hope present here. The fourth entry would have to address Napoleon's seizure of power and the animals that are killed in his public confessions. For Benjamin, these animals died because they spoke up or spoke out, a condition that Benjamin himself would not embrace. It might be an effective counterpoint to talk about how Benjamin revels in his apathy here because the last journal entry would have to take place in chapter 9, when Boxer dies. It is at this moment where all of Benjamin's supposed importance on being silent and being resistant to participation fails when he cannot save the one person he loves from instant death. He takes action, but too late. This might be a poignant way to close the journal entries.