I just went on a cruise leaving out of Barcelona in November. All my ports were different except for Athens. In Athens you may want to see the Acropolis and visit the Plaka area in Athens for shopping and grab a nice snack and drink.
I've sailed on the Century twice and I really like the ship. You will set up an onboard account with your credit card (or cash deposit, credit is best). All on board expenses of drinks, gift shop, photos, spa, excursions, will be placed on your on board account. You can also have your gratuities put on your account. During the last night of the cruise they slip your total bill under your door. If everything looks correct, you just leave it on your credit card you used to set up your account, and the bill will show up on your next credit card statement.
Drinks vary, but are similar to prices at nice restaurants. A martini can be $8-$9, beer $5, glass of wine can vary $5/$6/$7. You can purchase different beverage packages. They will have that information on their website and on the first day of the cruise you can sign up and ask them what all is included. Beer packages are separate from cocktail packages for instance. A 15% gratuity is added to any drink or package.