I tried using some of my american gas credit cards in europe, and they would not take them.
I have used my Visa CREDIT card for Autobahn/freeway tolls and NEVER had a problem over the years. I don't use a debit card and pin at a Autobahn.
We only use our Visa DEBIT cards to get cash, and the only problem we have had was when we did'nt follow up swiftly with our transaction, and the card was swallowed up. This is true in all of Europe! Don't screw around at the ATM withdrawal machine!
I have had no trouble using my Visa CREDIT cards in most countries in europe. When I fill up I always use a major station on an autobahn/freeway the first time in a country, or use a station with an attendant. They will help if you have any problems (and I don't speak any foreign languages!)
On our trip to Portugal last year, I could not get my VISA CREDIT card to work at the gas station. The attendant showed me that I had to push the "enter" button twice to get it to accept a card without a chip.
I have used my Visas in Italy, Sicily, France, Germany, Portugal, Austria, etc. with no problems. I pay for meals, gas, rooms, etc with them.
We always rent a car, unless we are only going to major towns served by rail. Sometimes when we go between countries we will take the train, or one of the lo budget airlines, and it will be much cheaper. (check whichbudget.com, etc for a list of lo cost airlines in europe)
Sometimes we can rent a car in one country, drop it off, and fly or rail to the next country, and rent again. Whe we did that in Puglia in So Italy we drove one leg, and caught a lo cost ailine for the return leg.
Make sure you check your rental car agreement, or better yet, call them, to see about renting in one country, and dropping off in another.
Buy your own GPS (that has EU maps pre-loaded), learn how to use it here, and take it with you. You will find this to be the most importnat asset of your trip!