[ilovelilo]

I can answer a few of your questions....
Port charges are $15 per day and your car is in a secure, monitored parking lot. The good thing about the car rental is you can come and go when you please at the port.....you can arrive when you want and leave when you want. The cost of transfers that Disney offers are rather high and in my opinion it is cheaper to rent a car, pay for fuel and park it than be on a scheduled transfer.....
If I had my preference, I would do the 4 day! It gives you that extra day to relax. And if you don't want to relax, there are tons of activities!
Once you do your first Disney Cruise, you will be hooked!

If you have the chance to do one, DO IT!!!!!