No one wants to deal with traveler cheques. You will spend most of your vacation just trying to find somewhere to cash them if you take them. :-)
ATMs are everywhere. Make sure you use a bank operated one as the others you might find in pubs or other businesses usually have high fees. Also check the withdrawal limit on your debit cards, ask your bank to increase the limit if you think it is too low for what you will be spending.
Yes, credit cards are used most places. I found it easier to pay cash in pubs and some restaurants. Always make sure you have enough cash to cover your meals and drinks.
Make sure to tell both your credit and debit card issuers when and where you will be so they don't cut you off thinking your transactions are fraud. And if the ATM or merchant offers to charge you in USDollars, decline. This option is called Dynamic Currency Conversion and allows the merchant or ATM to choose whatever exchange rate they want instead of being forced to use the official rate. You want to be charged in the local currency, otherwise It will cost you money unnecessarily!