I would most definitely not recommend washing your face three times. That's just going to strip your skin of oils, especially if it's an oil free cleanser. Oil is not what causes breakouts. It's bacteria that reproduce in your pores.
If you strip your skin of oil, it's going to produce MORE oil to compensate. I would look into oil cleansing if you can.
Instead of foundation, I would try a tinted moisturizer. I hate to sound like an old person, but teenagers have NICE skin. Even if you have acne, your skin probably does not need super thick foundation on it.
I would look for a good concealer and just use that where you need it, instead of coating your whole entire face with foundation. That said, I totally used foundation all through high school, and I regularly used Wet N Wild, or Covergirl foundations. I also bought those foam makeup wedges, and would use a damp one to apply my foundation, because it made it get good coverage and I didn't look like I had on a ton of makeup either.
Again, not to sound like an old person, but if your school has no rules about crazy colored makeup, experiment! Have fun with it! Get some colored eyeliners, or one of those big pallettes of eyeshadows and just play around with it.
Personally, I don't like the eco tools brushes at all. For me they feel really cheap and they're densely packed bristles, but in a bad way. They're not fluffy at all and I feel like I'm using a paint brush on my face instead of a powder brush! I would recommend the ELF Brushes out of the Studio Line. I have the flat topped one and it's soooo amazing. I have had terrible luck with their regular brushes ,but all the studio ones I've purchased have been really great.
I think for necessities, an eyeshadow pallette with lots of colors in it so you can figure out "your" colors that you love wearing and that look best on you. Brushes are good to have for sure, maybe those wedge sponges too so you can play with them, foundation, concealer. Maybe blush and some lipstick, but I honestly think lipstick looks weird on younger people because generally they have nicer lips and color in them to begin with, so I think it's a waste to cover them up with heavy lipstick! Lipgloss, maybe some bronzer?
Oh ya, a nice pair of tweezers, an eyelash curler, and a brush holder! But it's kind of tricky because everyone has a slightly different set up for what they wear.
But have fun splurging and getting fun stuff with your money, and make sure you look up coupon codes so you get the most for your money! ELF is always running specials for free items, or discounts, so it's good to get those too. =]