ok, (cruisemom42 and marazul) I will consider paying the higher air fare and the hassle of being in the thanksgiving chaos at the airport in order to arrive the day before. I thought going on the 24th would be less stressful and more likely to not have delays since presumably the bulk of people will have already flown to where they were going.
Regarding the baggage part...
As promised, I did stop by the airport today with my existing "carry on" and the BA agent confirmed what Vmax1700 said. According to the agent, it was too tall, so I will shop for another bag. Fortunately, the weight was fine, at 8kg, when I got back realized I forgot to pack pants and a pair of shoes, but even so, I think the weight won't be an issue, since they allow up to 23kg.