Boy, I wish you (or I) had asked this question a month ago!
We survived a week in Europe (Paris/Berlin) without using cash except twice. Push comes to shove, I guess I could've scrounged up some Euros one way or the other. I had this misguided notion that folks would accept the USD. You folks will never appreciate how wrong I was. My cash was unwelcome in almost all places - without fail - that I asked, both in Paris and in Berlin. We had oodles of $$ that we took with us and brought back. My wife used some $$ at Oslo airport at an exorbitant exchange rate to get some coffee; and I did the same in Paris to get some bus tickets, for an even more atrocious exchange rate. But we do have a few Norwegian Kroners and a couple of Euros to show for our effort - and the bus ride definitely saved us more money!
We were at the mercy of local restaurants and supermarkets that accepted our credit cards - we had five different ones between us - don't you try to tell me we were not well prepared! ;-) And Pizza Hut - yes, Pizza Hut - ripped us off by sneaking in a disclaimer that they had sought our permission to charge us in USD in spite of a nearly 4% commission on top of their exchange rate. I had first thoughts of complaining to Pizza Hut then decided against it - what if they revoke credit card acceptance for future customers based on my complaint?
Places that accepted credit cards:
- most places in the train stations and airports
- Indian restaurants (we had dinner both days in Paris in the Gare du Nord/La Chapelle area)
- Subway (Paris)
- Pizza Hut (Berlin)
- a restaurant where we got coffee and chocolate milk with a minimum of 10 Euros (Paris)
- a trinket shop near Sacre Coeur with a minimum of 15 Euros (Paris)
- Kaiser supermarket (Berlin)
- KaDeWe (Berlin)
- maybe most other restaurants would but we did not inquire
- pantry car in the train
Places that did not accept credit cards (though we thought they would):
- Dunkin Donuts (Berlin): this was surprising. They didn't accept credit cards even in the train station mall(s). We tried at a couple of different places.
I realized too late that I didn't answer any of your questions, did I?!! :-(
Re: 1: If you know the percentage that we lost in our cash exchanges, you will take the 1% fee and run with it :-) Here is a sample - I got just over 12 Euros in return for $20 in my sole cash exchange.
Re: 2 and 3. We were not asked for proof of ID anywhere that I can recall. The Capital One visa card that I used most often does not have a smart chip - it was not an issue. But we made all of purchases through a human.
FYI, I scanned passports of all members of the family, and copied them into flash drives. Also, ticket PDFs and airbnb host info went into each flash drive. Gave the kids a flash drive apiece hanging from lanyards and kept one for ourselves. We used those only in Paris. In Berlin, we were not out that long anyway.