Susan,
We did the full SA circumnavigation in January. You're in for a fantastic time, one of the very best cruises/itineraries we've ever done.

I'm not sure if it's too late but rather than do the one full day to Iguzu Falls through RSSC, I'd recommend doing it on your own the way we did...much better and 1/2 the price. We flew up on Argentina Airlines from Buenos Aires on a morning flight (taxis are so easy to catch to airport and I booked the RT flights on the internet) to Iguazu Airport on the Argentina side. We had a private guide set up who met us at the airport and away we went. He was terrific and with us all day and took us back to the airport the following day. We stayed overnight at the Sheraton Hotel (the only hotel within the park) with a nice balcony room with a head-on view of the falls. We flew back to Buenos Aires the next day. Those that went on the RSSC excursion had such a long day (and it was very hot!) and paid twice as much as we paid booking everything independently (including our hotel, lunch and a nice dinner). Many commented that they wish they had done it our way with the hotel stay. You can also go on the Brazil side of the falls, just make sure you bring your passport. Just some food for thought.

As for seeing penguins, you'll have lots of opportunities. We went on the Sparrow Cove adventure in Port Stanley, Falkland Islands and saw thousands of penguins. It was a great excursion but others who went on different ones all said they too saw lots of penguins as well. Lots of excursions to choose from along the way and they all sounded good.

Machu Pichu is an amazing trip too. Be prepared to feel light headed with the altitude but well worth it! It is magnificent.