I think you should buy all the mentioned materials above. The DAT material is the only source for PAT preparation as far as I know.
I also started studying in the beginning of the summer and had the intent of taking in the mid July. However, my nerves delayed the test until first week of Oct. I suggest for you to not schedule the test until you are realty. You do not want to schedule the test first and then have the goal of being readily by then. I knew I was readily with I was scoring the desired scores on the Top score practices DAT.
I do not suggest to only know what is in the Kaplan Blue book. The Kaplan book does a great job in covering the material in the DAT; however, if you do not completely understanding the explanation of the Book, you should have your college text for better coverage of the material.
I also felt that the DAT was easier then expected, but I would never change the amount of time I used for preparing for it.