Hi Kazzar,
I did this tour in Sept 2012 (with Travelsphere - although the itinerary is identical). It is fantastic and you will have a brilliant time I am sure! I wrote a review of it when I came back, so if you scroll down a couple of pages in the Reviews section you'll come across it. The weather should be warmer throughout than when I went - although I'd suggest a couple of long sleeved shirts and a fleece for Santiago/going over the Andes. I imagine it should be hot elsewhere. Highlights for me were tasting the fantastic wines in Santiago and Mendoza, the lovely scenery in Chile and amazing views while travelling over the Andes, the ranch visit in Buenos Aires and the tango show and everything in Rio! If you are offered a favela tour in Rio by the local guide, do go - you will be quite safe and it is a fascinating experience. But don't do it independently!!
Cheers,
Bob