Thanks for the reply; no I don't have land travel arranged, but I'm gonna do an overland trip, which is all arranged for in Africa...

I want to fly eco class. Why would these classes be sold out ? I am thinking of doing Paris => Nairobi around the 10th of October. And Jo'burg to Buenos Aires mid december.

How long do you think these kind of flights are booked in advance ? You are scaring me!

I am willing to simplify the route, inside the continents, but don't have much leeway otherwise, that is, it must be Paris or London => Nairobi or Jo'burg or CapeTown, and then Nairobi or Jo-burg or CapeTown => Buenos Aires or Rio or Sao Paulo, and then Lima or Mexico or Caracas or Bogota => Tokyo.

So only three flights are not really flexible...