Nice new toy, congrats
As far as you graduating hi school, be careful on the spending. I came into so,e money at the same age and had to learn the hard way. But it was a great learning experience. I also came into some money later in life, and I am much wiser with it now and the uses I have fore it. Many hard lessons were learned. I hope you don't find yourself in that position.
In the mean time, definitely get LR4, modify your car, get a boat, and start collecting watches, then do some travelling and enjoy life
And like Dave mentioned. A 70-200mm L series is one of the best investments you can make. And either the F4 or f2.8 are both tac sharp. If doing a lot of shooting inside, the 2.8 may suit better, but with the high ISO capabilities on the mark 3 that's sort of a non issue.
And don't be a stranger, visit often, and often with pictures