I went to Chile in November of 2013.
Buy plane tickets (inside Chile - from Santiago to Punta Arenas, etc) through LAN by signing in through Chrome/Incognito and picking your country as Chile (you’ll checkout in Spanish, but you’ll save like 100-200 bucks per flight - at least that was the case when we did it).
Santiago is pretty big but you can easily get around on public transportation and in cabs.
Atacama is beautiful and very dry - highly recommended if you have time. See the Valley of the Moon. If you want to do something absolutely nuts, climb Licancabur (the big volcano - 19,500 feet). We did a smaller hill next door (Cerro Toco - 18,700 feet or so) and it kicked our ass. Great mountain biking in Atacama, plus salt flats, flamingos, a bunch of other stuff - lots of hikes in the area and all the ones we did were pretty cool.
Chilean Patagonia is epic but very remote - you’ll definitely want to do the iconic W hike - we did the major pieces of it but you can also camp/backpack it (there are also lodges in the park though I think those are pretty expensive and will probably be booked - you might have more luck with one of the fancy places). Torres del Paine park doesn’t have much in it (t’s real wilderness) but Puerto Natales is supposed to be nice (one of the gateways to the park) - we didn’t make it there but you may want to stay there and drive into the park if you end up getting a car for a bit of the trip.