I'm not sure if this goes in the VA or AA forum, so I figured I'd stick it here and let the mods move it if need be.

I'm looking at booking STL-LHR, and found a fare on Expedia. It's STL-ORD on American, and ORD-LHR on Virgin. (and LHR-ORD on VA, ORD-STL on AA on the return). It's sold as one ticket, multiple airlines. Consider the fact that I have absolutely no status whatsoever on either airline when answering my questions:

Will AA transfer my checked bag to VA in ORD, or do I have to collect it and recheck with VA? (I know it's a moot point on the return since i collect it at customs and recheck)
Will I have to pay AA bag fees? I know the first bag is free for intl flights, but they're not flying the intl leg
If the AA flight to ORD is canceled or delayed and I miss the VA flight, is AA and/or VA responsible for rebooking me on another flight to LHR, or am I up a creek? Ditto for the return trip into ORD.
If it's booked on Expedia, can I go to the respective airline's site after booking, and with the PNR, choose my seats ahead of time, or am I going to be stuck choosing the least crappy middle seat (as if one middle seat is less crappy than another) at check in?

I'd really like to fly Virgin across the pond, but not if it's going to leave me stranded or leave my bags in Timbuktu. Thanks.