I work at MIT's admissions office and am a graduate student at Harvard...
Answers to your questions 1) If its too long...YOU NEED TO CUT IT DOWN. The word limit on your PS and essays is a test of your communication skills. If you are over, it implies that you have no focus in your writing and that you are just trying to give them as much information as possible. As an admissions counselor, I would think that you didn't understand the question or you just cannot communicate effectively because you have no idea what is important. Some schools now even have automated systems that will just cut off your essay at the word limit. I also understand if you have a lot of examples, but you need to understand how to use the examples as a venue to present yourself, as opposed to just explaining the example. It is also important to know how much detail to include. If it is too detailed, its unnecessary because you will lose the big picture and bore the reader. But if you don't include enough, then your writing seem like you are making things up.
2) If the school only asks for essays, then only do essays. If you put additional unnecessary information into your application, it is a waste of time for the admissions committee, negatively impacting your application during the review process.
3) I actually offer writing and editing services. You can email me at tinaxue@mit.edu or tinaxue@fas.harvard.edu. I can give you some samples. My customers in the past have been accepted by the top 10 business schools. This year, some of my customers have already received interview offers from Harvard and some other schools. If you want, I can take a quick look at your PS and essays and give you immediate feedback on what are the most obvious issues for free.
you should write the optional essay if the topic benefits you. Sometimes...for example, if you have no leadership experience...you should not try to write an optional essay on leadership