The answer to the damage question is: you don't want to find out. Anything involving rental cars and insurance is a huge pain in the patoose. As far as the rental car company is concerned, yes, you personally are liable for damage to the car, plus the "loss of use" while the car is in the shop getting repaired. Sometimes they want payment immediately. Of course, only a moron would rent a car without using a credit card that offers collision/damage insurance (please pardon my strong language, but I get really angry that the rental car companies charge people $10 a day for coverage that they already have). So in the end you won't have to pay for damage to the car. However, read the fine print in your credit card agreement (it might be in a pamphlet titled "Additional Program Information"). Most of the rental car coverage is secondary, which means that you have to file a claim with your personal auto insurance first. So first you pay the rental car company, then you file with your personal auto, then with your credit card company. It's a pain, and your personal auto premium might go up as well. However, the credit card company typically will pay anything your personal auto won't cover, which is a lifesaver when it turns out that there was a huge flood and your $15,000 rental car got totaled. But I cannot express enough the importance of reading the fine print for your specific credit card.
However, I would suggest that a far better deal is to get a one-way rental from the airport (MCO) to the port. We are paying less than $25 a day, and we don't rack up rental and parking charges while on the ship. I highly recommend it.
Walt