I find it interesting and amusing that your location is "Since my sophomore year in High School, when I started experimenting with Scriptwriting."
Anyway, I was in your position, and I'll tell you everything you need to know. Okay, well not everything, but, well, okay just read.
First of all, at the best schools you need a strong academic component on your application as well as some artsy potential. These schools are "highly selective", and will take your academics into account on a large scale. Some of these schools are, but are not limited to:
NYU Tisch School of the Arts
USC School of Cinema & Television
UCLA
Emerson College
Chapman University
Now, at most, they will tell you that there is no cut off GPA. I'd comment that to have a reasonable chance of admittance, you'd need at least a 3.5 unweighted GPA and at least a 1300 (old scale) SAT score. Granted, some, or even many have been admitted to these schools with lower stats, but if you find yourself qualifying these standards, you're well ahead of the game.
The essay is critical even with great stats. Many apply to these schools with great grades, but it is the essay that will inevitably put some kids into the acceptance pool and others into the rejected pool. Write a good, honest, passionate essay, and don't try to impress them with your writing. Be sincere, that's what counts.
To answer your first question, I once read that a good application essay can heal the sick, but not raise the dead. If you don't get the metaphor, film probably isn't for you.
As much as I've read, college experience doesn't at all highlight real world experience. After college, expect a few years of having a day job and stealing food. Many live like this, only doing film as freelance stuff aside from an 8-5 job they picked up after college. But, if you love what you do, and you're dedicated, it doesn't have to be like that.
For me, the job security concern was the biggest (and only) reason preventing me from declaring a major sooner. I have always loved to tell a story, and have made short movies for years. My parents and conscience told me to be realistic, so for a while I thought I'd be going to a good state school and majoring in something a little more broad. This didn't last.
On my first day with my college advisor, she pryed out of me my true interests. She simply asked the question, with a lot of enthusiasm, "Why not you?" An entire scheme of things went through my head. For example, I love old people. The neatest of them, the ones who told engaging stories that kept you listening, they didn't take the safe path in life. They have stories, lively stories about their early years. Stories about how they starved for a few years while trying to make it in their given field, or stories about how they felt once they finally got their big break. I want to be able to tell those kind of stories. God spare me a safe journey.
If its your passion, don't let anybody else tell you to take a less precarious path. Do what you want, if you're good at it. You've got one life. Do something different.
I hope my mumbo jumbo helped. I may sound like I'm preaching, or like I'm being cheesy, but it's honestly what I feel. Your decision is a huge decision, but that doesn't mean it has to be a hard one. Be true to your interests. That's what I believe at least.
Good luck!
Tyler
"And whatever you end up doing, love it!"- Alfredo from Cinema Paradiso