I agree that he let himself be tricked into going to prison. I’m not sure why yet, but I’m sure he had some reason. At first, I thought it was because being in prison unknowingly to Charming and Snow allowed Rumple to retain his memories, but since the producers have confirmed that he didn’t remember to Emma arrived, I suppose not. Although maybe being in prison did help tamper the curse a bit though, so he could put in the memory switch of Emma’s name and know that it would work later on.
Also while I do think he had everything carefully planned out, I’m not sure about Rumple being able to see the future or him having to do with Henry’s book at all. I think he’s just very good at predicting people’s future actions based on their personalities and previous actions. So he can almost always count on Regina acting impulsively and for her own interest, while on the flip side, he can usually count on the Charming family to act heroically, so he can use that into manipulating what is best for him like having them all be pawns in the curse and finding Bae without them ever realizing that he’s doing so.
As for the book, during the first few episodes I thought he was the author, but I don’t believe that he is now since August knew about it somehow and what kind of paper and typewriter to bring to add new information to the book. I think the only way he could have known about that type of information is from the author of the book. Then, I thought it was either the Blue Fairy or Bae helping August, but after the season finale, I don’t think the Blue Fairy remembered anything about her past life. So I think only Rumple’s son is the one who helped write the book and planted it in Storybrooke. He may have taken out the chapter about his father, if that’s what happened since Henry didn’t know who Rumple was earlier on in the season, not to help his father, but to make sure that there’s very few people who know that Rumple had a son that way he can use that to his advantage later on.