I already have an American Express, as many do from Delta. I take it among other cards as it is Zero FTF. I also have used it frequently in Europe, have never had a problem with a rental car company or hotel in a larger city taking it. I typically pay cash for meals, but notice that many restaurants and even shops do take AE, many more than when my business used the card a decade ago or so.
As for approach...my only concern with your initial proposal is that the duplicate cards are on the same account, while they can freeze a card, they may also choose to freeze the account, making the other card useless as well. Same as if the account "detects suspicious activity" and places a hold on both cards. I prefer debit cards from two different accounts and credit cards from 2 or 3 accounts, at least one with a PIN for cash advance. Also, spread them out physically, while a money belt/pouch is great, do not put everything in one place, I keep a credit card in a hidden place in my carry-on for example.