Hi guys,
Just a short note to say I ended up booking the trip as follows:
NRT-HKG-LAX-SJO-LAX-ORD-SEA-JFK-SCL-IPC-SCL-EZE-xORD-AMM-TUN-AMM-FCO-HKG-KHI-HKG-NRT
For a couple of reasons, I was planning to go from South America to AMM via Europe, but the flights didn't work well (no availability on the BA option; bad timing with Iberia), so I told the agent about the ORD transit option. He said he would never have thought of that, and obviously I wouldn't have either.
I ticketed the reservation through AA Japan directly, after getting some advice from Gardyloo. It took a while to reach them, but they were efficient when I did.
I'll pick up this ticket and begin the journey on March 26, after trekking through India and Bangladesh for a couple weeks beforehand.
I'm really excited and I appreciate everyone's help here! Thanks again.