Yes. If you take the exam 09/02/21, your score won't come out until early October. Most schools won't review your application until it's considered "complete" which includes your primary, secondary, MCAT score, and LORs. There are a few schools, here and there, that will look at your app and even issue you a II before your MCAT, but very few schools do this and its too risky given how freaking competitive everything is. Plus they will consider that MCAT score before issuing an acceptance.
Yes. If you decide to apply this cycle, you can note on your primary application when you plan to take the MCAT. Schools will see this and will know when to anticipate your score. Once your score is released it will automatically be sent to all the schools you listed on your primary.
If you decide to withdraw after seeing your MCAT, you will be considered a re-applicant at schools that received your primary if you apply to those schools next cycle. If you hypothetically withdrew and had new schools next year, you would NOT be a re-applicant for those particular schools.
All in all, you plan is incredibly risky and naive. If you are gutsy and do go for this, I suggest you wait until your MCAT score comes out in early Oct. If your score is good, submit your AMCAS primary ASAP and you will be verified within 1-2 days. If you pre-write your secondaries, you can submit by end of first week of Oct. and be complete. If you get a bad score, don't apply this cycle you save yourself hundreds of dollars.
All in all, this is a BAD IDEA.