Regarding tipping:
When I am in Europe, I try to pay with credit cards as much as possible, because I get a better exchange rate that way than I do at ATMs. I still take out some cash for incidentals.
At restaurants, if you pay with a credit card, in most places there is no option to add the tip, and I often don't have any small bills for tip. So I don't leave a tip. When I was in Scotland this past spring, restaurants in Edinburgh allowed me to add tip to the bill, but not at all elsewhere in the country.
Here in Mexico, if I pay with a credit card, they ask me if I would like to add the tip to the bill before they run the card.
Regarding language
As a solo traveler, I have on occasion been seated in a restaurant with other solo travelers, often Europeans from other countries. The Dutch travelers I've met this way didn't know a word of Italian when dining in a restaurant in Florence. They spoke English unapologetically.
Here in my Mexican community with a large population of expats and immigrants from the US and Canada, servers at restaurants will commonly address me in English, even if I speak Spanish to them. They appreciate the opportunity to practice their English. And often their English is much better than my Spanish, so it is silly for me to struggle to come up with the correct Spanish phrasing when they speak fluent English.
Regarding "Go with the flow":
This is probably the one piece of advice from this article that a lot of us on this forum, in my opinion. should pay serious attention to.
It drives me crazy on this forum when people ask for advice about an itinerary that has almost every hour of every day scheduled. Many on this forum are most guilty of trying to cram so much sightseeing into every day that they forget to relax and have fun. And don't use the excuse that we have limited vacation time. You can enjoy your travels at least as much if you do sightsee less and smell the roses more.