Well, most active and passive basses when you don't use EQ are very similar. After all, the front end of your head is basically an active preamp! An active bass merely moves part of that EQ circuit into the bass where it more convenient to adjust while you are playing.
In the Common Application, it says that the Personal Essay should be at least 250 words, and attached on a separate sheet (presumably, if you're submitting it online, you attach a one-page file).
Well, it really depends on what the topic is and what grade level. But, I would say around 4 at least: 1 for the introduction, 2 for the body paragraphs, and 1 for the closing. All in all, the essay should be as long as it takes to answer the question. My best advice is to ask your teacher how long they would like it to be.