Hi Julie:
I went in November on the Dawn and had the best time. Personally, I found that doing things "on your own" may be best. We didn't sign up for any of the excursions only because we didn't want to feel "too limited." When we got to Cocoa Beach, we had family pick us up and spent the day in Epcot. South Beach, we took a cab from port to the beach, which was perfect--we may have paid $17-20. There is not a whole heck of a lot to see (I thought) in South Beach during the day, but if you want to just sit in the sun, you can't beat it. Atlantis--again we took a cab (which turned out to be a stretch limo that we shared with six other people--$4 each!) to Atlantis. Atlantis can be tricky to get around. We paid for the Aquarium and limited access to the grounds ($50 each) and you are not allowed by the pool area nor their private beach. I hate to say this, but we snuck around and managed to get to the Lagoon and the beach--stealth pays! I have heard of other people arranging for a room at a smaller hotel nearby in order to have true beach access as well as a place to change...and some may provide more access to Atlantis. Unless the itinerary has change, your time is limited at Atlantis--use it wisely and enjoy! There are plenty of wave runners, parasailing, etc. In terms of weather conditions, you should check out weather cites offered by Yahoo or just poke around on the Internet and see if you can at least get a general idea. I would imagine it will be warmer than it is up here!
If you have any questions, let me know. Sorry this was long but it really was a great trip!