Several answers to your questions.
As a first time cruiser, you can begin booking dining, spa and excursions 75 days before your cruise. Currently is is too early for anyone to book these.
I do not book excursions in Key West as it is so easy to wander around and see things on your own. You can often find coupons for things like the Conch Train and museums that will save you money over booking with Disney.
In Nassau, the Blue Lagoon excursions tend to get better reviews than Atlantic, but I have not done either. I can recommend the Chocolate tour at the Graycliff hotel if you decide on something non-beachy.
There are a limited number of cabanas on
Castaway Cay, and will most likely be taken by concierge and platinum cruisers. If you are not sailing concierge, you would be very unlikely to be able to secure a cabana as a first time cruiser. Please be aware that there are plenty of chairs, loungers, umbrellas, hammocks, etc. on Castaway Cay, so even without a cabana, your family will be able to find a great spot.
My cabin in on 7 and my sister's is on 5.
Mine love making new friends - not a shy bone in either of them.
You can also go find an old, out of date thread and post your 8 there.
