OK so I'm posting about stuff as it pops up in my lagged brain. Credit cards - I used them everywhere with almost no problem. Note I said almost.
For shopping, very simple. Make sure you have a contactless card and just touch it to the appropriate place on the terminal. For restaurants almost as simple, look for the right place to touch. Sometimes they would insert the card to have the chip read and then, you will have to sign. No one thought it was a big deal. As you probably know, every restaurant brings a wireless terminal to your table and you do the deed right there.
Read the screen carefully before you accept, a few times the machine was savvy enough to ask if I wanted to do DCC (do some research on that if you're not hip to it), I knew enough to know that most people advise against it so I would reject it and ask to be charged in euros.
Funny experience buying metro tickets from a machine. I had read beforehand that these machines were very particular about only taking chip and PIN cards so I was standing in line for a human but it was taking too long, so I took a chance and tried the machine. You push the appropriate button and it talks in English, no problem. After I inserted the card it wanted a PIN as I had feared, I hesitated before trying to cancel and the transaction went through without the code! So that's a YMMV situation.
Luckily the one problem I had was with a taxi my last night there at the airport (that is a large amount). I gave him my Capital ONe card which I had been using all over Paris and hoped the contactless would work but his terminal wanted a code. Well I knew that card didn't have one, so we cancelled and I gave him my Andrews CU card which I specifically got for the PIN. The terminal wanted a PIN and I entered it and the deal went through and ... then he said I had to sign. At a certain point it's not worth questioning. I'll wait to see how it turns out on the statement.