Don't worry too much about the diagnostic test. You have much space to improve but you have much time to study for it too. 40 plus practice exams are actually a lot. Each one will need at least 2.5 hours to finish and then another 5 - 6 hours to check and redo. And you cannot just do LSAT all the time. It would be good to practice and study those 40 exams in 6 months. 6 months should be more than enough. If you can finish the bibles in one weeks, you should have a pretty good reading ability. Just read the bibles one more time after you finished 10 sets also practice exams. You will learn much more from those two books. I never finished reading those books. But I can imagine how those books can be helpful in some occations. Good luck.
Most people here started from a higher level. So most actually do not have experience with that state in my understanding. I really do not know how to study when one's vocabulary is limited. Sorry.