Hey Dragon,
Once you hit the submit button, your application is complete. The only change allowed is to update your grades from the Fall semester in December/January. So before you submit your application, you will need to have your LORs submitted, observation hours confirmed, and everything else entered. Transcripts can be en route, but if you complete it early enough, it shouldn't be an issue.
As far as the essay, each school has different questions. I applied to EWU, and they had a short prompt asking why I wanted to attend their school. They only gave a couple hundred words to complete the prompt. All the other school I applied to did not have much of anything for specific school questions. So for the most part, the one to two page write up encompasses most of what you will be allow for a personal statement to most schools.
Applying to Baylor was a different story though. Because they wanted to understand why I wanted to be a PT and a PT in the military, they required two essays. But that is a school that does not utilize PTCAS. I am unsure if any PTCAS schools want much more than the one essay.
I hope that answers your questions. Good luck!!!
