Have fun in Paris!
I've always had great service at SL, and spent a significant amount of time smelling all the paper strips. They all speak english well, of course. For fun, in Paris I always use a horrid italian-french pidgin, with english thrown in; never any problem. When you isolate the perfumes you like, you can ask the SA to put the actual juice on your skin. The first time, as I was undecided, the SA even told me to keep smelling through the day so that I could see how it evolves... the first SA who doesn't try to close a deal right there.
They don't give samples however. If you buy something, they'll give you a set of wax samples of their entire collection. Very occasionally, they have a vial of their export, but not always. You should ask of course. Incidentally, remember that some of the exclusives are also available in the export collection (eg Borneo, Tubereuse, MKK, et al) so you might want to concentrate on the exclusifs that haven't made to export (eg Sarrasins, La Myrrhe, Iris Silver Mist, Boxeuses, Fourreau Noir, Fumerie Turque, etc.)
Caron: I only went to the avenue Montaigne one, and service was good. Our Caronian Larimar should be able to help you here with plenty of suggestions. I don't know about the average cost of the extraits. I got 8ml of Tabac Blond in the plainest bottle, and I think it was something around EUR 85, and in any case below EUR 100. But I think prices will vary depending on the scent, and the bottle.
Dept stores: for perfumes, niche are equally divided between Lafayette and Printemps. Conveniently, the two huge department stores are one next to the other, so there's no need to choose. Probably Lafayette is a touch bigger.
Since most of what's at Sephora can be found this side of the ocean, you shouldn't probably bother. Anyway, Sephoras, Marionnaud, and Nocibe (the three largest perfume chains) are sprinkled all over Paris, should you have any need. The advantage of Champs Elysees stuff is that it is open on sundays and late at night.
Re: Goutal and Artisan, again, since all can be found here, perhaps it's not worth. Besides, there are very many great perfume stores within a couple of minutes walk from the Goutal store, I'd rather save my nose for those. (Two doors down is JAR, for instance. Perhaps you might not want to dump EUR 600 for 30ml of perfume, but if you don't see anybody in the store sniffing, you should enter and sniff - it's quite an experience. You sit down at a table etc etc Save your nose for Eclair).