Since we all love research, this article was incredibly helpful for me in crafting my personal statements without putting myself at risk for rejection!
http://psychology.unl.edu/psichi/Graduate_School_Application_Kisses_of_Death.pdf
To answer your questions:
1. No
2. Do whatever is required, but not more. If the school doesn't require the psychology subject test, odds are they will do no more than glance at it when reviewing your application.
3. Increase your chances? No, and thinking it will help you will only hurt you. Make you interesting? Maybe, if you write about those experiences in a way that invites dialogue and fits into the larger narrative of your personal statement.
4. Yes, all transcripts. Sometimes they'll only request official transcripts after you've been interviewed and admitted and only require unofficial transcripts until then.
Good luck!!