1) Don't know but I believe Sabre (AA's reservation system) cannot contain a PNR with no AA segments, in which case AA cannot store the PNR for you. The airlines can force you to ticket with the airline flying the first leg (presumably BA in your case) but generally don't. AA may refuse you unless you fly either trans-Atlantic or trans-Pacific on AA; in the past AA has been very accomodating but they have been getting lots of work with reservations with no AA revenue and this is wrecking the service for all of us; the AA RTW desk isn't what it used to be. Personally I have always ticketed with the airline getting half the RTW revenue.
2) no changes to flights prior to the first international sector (not applicable if starting in WAW as all flights from WAW are outside the country).