I'm afraid it isn't a good idea.
You cannot predict how close to your EDD that your baby will arrive. (And IMHO--though may be controversial, an induction or scheduled c-section so that you can make your scheduled vacation is not a good idea either as that will become a valid concern as you come to the end of your pregnancy.)
You are not allowing yourself any recovery time and you are presuming the perfect conclusion to a perfect pregnancy.
We did take DS when he was that little (just over 6 weeks maybe, I would have to go dig and find out). We live within 90 minutes of disney and we had our passes that were expiring. The trips were not planned in advance, but rather--I felt good, so we went after he was 6 weeks old.
My biggest issue though--is more over what you cannot predict and the temptation to want to fool with mother nature to make a voluntary trip.
I'd push it out by a couple of weeks or so at a minimum (8 weeks past your EDD) so that you know the baby will be at least 6 weeks old.
Trip Insurance would cover any unexpected issues and permit you to cancel your trip if something unknown happened.
Maybe also consider going earlier than December. Perhaps when you are 6 or 7 months pregnant as a last hurrah with your dd as an only child.
With my son, I traveled with my Moby Wrap--it was a lifesaver as it permitted me to walk and nurse and permitted him to be close to his mommy like he liked. I enjoyed being out and about and the family had fun riding the rides that he couldn't go on.
I would bring ponchos or something to cover the stroller in the event of rain. You must park them in most places and if it got wet, it is useless for the baby.
(and in case it wasn't clear, I am not against you traveling with a 6 week old--it is more of being unable to predict and treating babies birthday as a deadline to make a trip.
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