Your biggest challenge with any RTW ticket is going to be fitting as many of your destinations as possible within the 16-segment overall limits of the ticket. You have to include segments that you need to connect to other places - for example you can't go Cairo > Johannesburg on any Oneworld carrier; you'd have to go via Madrid or London, so the Cairo - London/Madrid segment uses up one of the 16.

Similarly, any one-way land or surface travel (e.g. land at Santiago, continue from Lima) also consumes one of the 16 segments, even though you're not flying with it.

This is a common problem with 6-continent RTWs. By the time you've subtracted the 6 intercontinental segments you're left with just 10 flights to places that aren't intercontinental gateways, or less than two "extra" cities per continent. By hopping around any continent for more than 3 flights, you've effectively removed another continent altogether, if you get my meaning.

In doing your research I'd suggest looking at the various "air pass" products sold by Oneworld, e.g. the Visit South America airpass, and think about using the RTW ticket as a "backbone" for expensive flights (e.g. Easter Island) and using local airpasses, or cheap local airlines, for shorter trips, saving the 16 RTW segments for the long haul segments. Where could you go quickly/cheaply once you get to X continent?

It's a tough but fun process - good luck.