Dartmouth 06 here.
I would strongly advise that you reconsider your first term courseload. If nothing else, just to see how you adjust to trimesters. Although we operate on trimesters, we don't really do less work than a semester, it's just compressed. And you'll be in honors courses as well, so there will be an added degree of difficulty. I've heard great things about Chem 10, so I would go with that. But I would honestly try to avoid doubling up on the sciences in the first term.
Your first term at Dartmouth will be a really exciting one and you want to be sure you get off on the right foot. Take one of the sciences, take something in your major, and take something ridiculous just for the fun of it.
As far as your major choice, pick something you love. It goes a long way towards taking the edge off, when you have a chem exam or a physics exam coming up. I was an English and Creative Writing major. I didn't take any econ courses, but I've heard mixed reviews. One of my friends majored in Econ and it was very easy for her. English courses however, were not her friend. You have to really go with what fits for you. I probably wouldn't have done too hot in Econ, as I didn't have a passion for it, so I stayed away from it. I remember people saying early on during Freshman and Sophomore year, that the intro Econ courses are really challenging. After that it supposedly gets better.
Congrats on your acceptance though.
I loved my four years at Dartmouth. I'd do it again in a heart beat.
Go on a D.O.C. Trip!
OK. I'm done.