The first foreign language in all of Europe is English. In all tourist destinations you will find people speaking it, often enough of them that you might think everybody in the country can communicate in English.
In a few months you will not have time to learn other languages, but try to learn the local version, for each of the languages, of 'good morning/day' 'thank you' and 'goodbye' and use them with a smile.
The mistake most people make is trying to do too much in too short a time. When I see your list of 5 countries I hope you have 5 weeks at least. Typically traveling between countries costs a day when traveling by train, most of a day when flying and leaving you too tired to do sight seeing in what will be left of the day.
A day in Greece will cost you 3 days of your vacation, one to travel each way and one to sight see. Get out a good travel guide, libraries stock them and you will often find them in second hand book stores, and work out what you really want to see and whether it is worth it to miss two full days sight seeing for the time you have there.
Each of the countries you mention uses the euro. Often the cheapest way to get euros is to use the ATM wherever you are. How much you pay, and whether you need to pay at all, depends on the contract you have with your bank. Contact your bank and find out whether your bank card is ready for use abroad and tell them that you will be using it in Europe, (and tell them you arrive the day before you actually do, as some forget the time difference and have you 'arrive' half a day after you actually do,) and get them to tell you how much each use will cost. Some banks allow you to do all this online, but if in doubt, just talk with a real person of your bank. Your own bank should be able to get you euros to start you off, €200 would be a good amount, otherwise the exchange office at the airport even though it might be a bit more expensive, or the ATM in the arrival airport.
Do carry some of your own money, like $200, in case your card fails or you have other problems, cash exchanges are more expensive than getting money out of the ATM but having real money will always work better than money in a bank you can not reach.
And if you do have a credit card, bring it. The best will be if it has pin and chip, but any CC will be useful in some cases.