Don't use a credit card at an ATM to withdraw cash. That counts as a cash advance, and on many cards, will result in an interest charge from the moment of withdrawal. Use an ATM card or debit card.
The parking is safe. I'd be concerned about finding a parking space for that large of a vehicle in the garages, though. Might want to call ahead about that.
DCL isn't sailing from Port Everglades yet, so there's no shuttle from FLL to MCO. I also doubt that service will exist when they do sail from Port Everglades.
I use the Solarium hot tubs (and the pool on M-class) from 4:30-7 or so precisely because fewer people are around.
If it's adults only, it should be adults only.