1. Montly payment is only relevant to how much you're financing, and for how long, and how much interest.
2. I wouldn't say its the best car for a new college student, mainly because it is a hybrid, and they do get costly to repair if there is an issue, and it's highly expensive (especially because the 2010 model just dropped, and they're highly wanted even in this economy which equals a price mark up)
3. What do you mean by percentage? I'm guessing you mean in the commercials. Those are APR, or interest added onto the car. Usually fi you have really good payment, you'll get zero or a really low APR for 3-4 years, usually the longer you finanace, the higher the APR. Since you're 17, and you can't get credit, i'm guessing you're going to be finanaced under your parent's credit?
And as for down payment, it's what you put down intially on the car. Most dealers want this, and it's usually 20 percent if you have good credit, or if you have bad/no credit, a lot of dealers mandate 50 percent down.
What you should know:
Hybrids are the biggest thing right now in the auto industry, therefore you will be paying big bucks for one b/c a lot of people want one. You can always get the older body style for a cheaper price, but resale value is also less b/c of hte new body style change, it all depends on what you need, and what you can pay for, and how long you plan to keep the car.
*MSRP/Sticker Price/Asking Price is always before tax & licensing fee. Always ask for an out the door price before you settle on a car/dealer.
* Sometimes, you can find better financing from a different credit company, so you can finance with that finance company, and buy your car in cash, which will also come with a discount.