Thank you both for the advice. I actually called LAN twice and the AA RTW desk twice before and they all said there is no flight currently listed, so no way to start the trip there. They also said it would be impossible to change my route later without reissuing the tickets at the latest fare and rule set since it would be my first flight.

I don't really have a problem with either of the options I listed. The bus from USH to PUQ is about 12 hours and a flight USH-AEP is only about $150 US. I just wanted to make sure I knew what all my options were before making the decision. Thanks again.