Okay for a short trip I would definitely spend more time at the Orsay, the Louvre is fabulous but I think for a short trip you'd have more fun just hitting the highlights - Mona Lisa, Venus de Milo, Winged Victory.
I wasn't crazy about Monrmartre, too touristy & crowded for me. Norte Dame is really beautiful and you can walk up to see the gargoyles, its also close to Saint Chapel which has amazing stained glass - we were really happy we went there.
You'll want to go up the Eiffel Tower for the view, but get there as early as possible because the lines are long. You can also get a museum pass at the airport for going to the museums - the best part is you skip the lines, you just flash your pass.
I would metro to the l'arc de triomphe, rather than walk up the Champs-Elysees - frankly the Champs-Elysees used to be a super high end street for shopping but it just isn't so much anymore. You can metro there and go to Louis Vuitton - there will probably be a line outside - and Cartier and Sephora, other than that there wasn't much. For shopping you must see Hermes on Saint Honore - its an experience. Its also close to Lanvin and
Gucci, Goyard, Chanel (which is wierdly small) and some others. Cholette is interesting but a little out of the way, I would only go if you're into that sort of fashion and willing to spend the money.
The Galleries Layfette is insane - its like a huge mall packed with people. I didn't like the crowds but I did buy a little something there from the Chanel boutique, which was less crowded. If you go make sure to get a discount coupon from information - along with a map - the discount didn't work at Chanel, but if you got something from a non-boutique it should work.
