That's a great start. Do make some short term goals for yourself. Because sometimes it's easy to get set back when you think... WHOA I have how much more to lose? And people get frustrated with losing slowly.
I think your long term goal is quite manageable though, because in most cases people can lose at the rate you have planned to lose 73 lb in a year. I started about a year ago, at about your weight, though I'm a bit shorter!
Did you come up with an eating plan yet? Exercise is great, but at least for myself, it does nothing if I don't eat proper. I try to eat only nutritionally wholesome foods, and I am a calorie counter, which I would recommend, however there are lots of options and some people do fine by other means. You'll have to play around with it to suit it to you, depending on your activity level and your own physical body structure. There are different forums here for a lot of different styles people use to lose weight so check them all out if you're curious.
Oh, PS. I know you said you are 18, but come join us in the 20-somethings board if you want to get in with a community of people your age!
http://www.3fatchicks.com/forum/20-somethings-56/