If you plan to do this trek, I even would warn you not even think of buying any other book than Lonely Planet's Trekking in the Patagonian Andes. All my Patagonia hikes I did with this book (have all 3 editions by now :-). The descriptions are reliable, the maps accurate, the trek hours as well (I knew at any point how much to add to his hours to meet my pace).
Once I thought to increase my Patagonia library by buying a german hiking book - even from a well known alpine publisher. What a waste of money !!! They seemed to have copied Clem on their trails, added their own fantasy here and there and I was either quicker or slower than them??.
"Trekking in the Patagonian Andes", 3rd edition, by Clem Lindenmeyer, ISBN: 186450059X, 296 pages, 36 maps, USD 19,99.
The author, Clem Lindenmeyer has hiked Patagonia for years, and each edition adds some new treasures to the known hikes.
(and no ? neither Lonely Planet nor Clem Lindenmeyer pay me for this :-) )
We were extremely confused when trying to check with CONAF (Chile's National Park Organization). Usually, when you hike a not so popular trail, you let them know what you are doing. Even for the very well trotten Circuito in Torres del Paine they make a big thing registering your passports and all that.
We have tried to get in contact with CONAF in Coyhaique, but the place was abandoned, and nobody really could tell us where the rangers are. Plus the hut, which should be close to the trail entrance at Las Horquetas Grandes is not inhabited.
So let someone know, you do this hike, and I can only recommend to book yourself in Las Salamandras in Coyhaique, as the owners are well experienced outdoor people. They will check by radio with the people in Villa Cerro Castillo, and start looking for you if you don't show up at the proposed time.
And please learn from our experience - the trail is awesome, I would do it again and again and again - but due to the weather you never know the trail situations.
When we did this hike, the rivers were not carrying much water. We saw it with Rio Turbio who was described as rapid big river - we found a little creek running in an enormous riverbed.
So be aware that depending on the time of year or progress of spring and thus melted water, all rivers might carry much more water than on my pictures.