Your flight will include one free checked bag, assuming you don't select a 'hand baggage only' fare (which are clearly marked during the booking process).

You can enter your AAdvantage number into the reservation through the booking process online.

You can choose your seat for free from 24 hours before departure at online check-in, or from 7 days before departure (if oneworld Ruby) or from the time of booking (if oneworld Sapphire/Emerald). If not eligible for free seat selection, you can pay to choose a seat before online check-in.