Congratulations on taking the big step! I would recommend taking as many, if not all the knowledge exams as you can in this time before you start. Yes, there is time built into the program for you to study, but those times may be short, and you may find the time you would be spending studying for the knowledge test better served preparing for the flights or check rides. You will also have a leg up on having been exposed to the material and find it easier to stay ahead and maximize the time you are flying into learning new things faster, than if you were seeing it for your first time.
I personally completed all the knowledge tests early, and would have it no other way. I spent a few weeks before I started really grinding out those tests, it was unpleasant at the time, but I am so happy I did before then. The added benefit was I was in the “mode” to take test and used to the FAA knowledge test questions. Plus, the tests really build on themselves as you progress through them. I found that helped me retain the material better by going over it and over it prepping for the test: example, I was very poor at weight/balance and Time/speed/distance problems when I started, by the end of the test, I had really come to enjoy those long problems and still do to this day (working on my CFI now).
Also, in the last week or two before you start, I would put some time into going through the POH and the Supplement for the aircraft you’ll be flying. There are a set of questions in the back you should know all the answers to. If you can get those down before you head out to the airplane the first time, your first preflight will be a lot more meaningful.
I guess a little disclaimer: I can nerd out pretty hard on this stuff, and these are just my views.
But best of luck to you!