Quito to Rio

HI guys i am really sorry if this is a regular question, i have had a look and cant find anything specific to help me on this. me and some friends are planning a 3 month trip from quito to rio or maybe buenos aires depend on what people think about the time scale. I have travelled round south east asia and europe before but no where on the size of south america and am struggleing to work out relasitically what we can do in 3 months. a potential plan was quito include a little bit of amazon, lima and machu picchu, lake titicaca la paz salt flats, buenos, and up to rio and some places on the way. we were gonna try and get some cheep internal flights to speed things up, in argentina and brazil, but were wondering how long in advance u need to book these or can u just turn up like buses and book on the day? ideally we would like to do patagonia to but i think this will be way to much.are we being un realsitic with time scale? i have read u need a month a country? any reccomendations? we will be travellin 9th sept till 1st dec. this is a good time to do those countries in this order? any help would be appreciated or if someone could kindly point me in the direction of the right forum, that would also be appreciated. thank you for your help. jez