We live abroad. Been doing it almost 4 years and will continue to do so for what looks like some years to come.
I can give you some practical advise. Though you may blow it off (as I did) as a minor inconvenience, language barriers are a huge huge
problem. I always expected if all these people in this country could speak this language, if toddlers on the street could do it--so could I.
Yeah....that's not quite how it works out. The older you are the more difficult language acquisition becomes. You'd be amazed as to what I cannot do here
because of the language issue: I cannot make a phone call for a haircut or dentist appointment. I have to find the [only] providers who speak English and GO THERE to arrange the service. I have cats who need shots and spaying but it isn't done because I can't find an English speaking vet. I studied for a year and work among native speakers only and yet can still blurt out only the most miserable mispronounced phrases. It is far far more difficult than you think.
Believe me here, banking and bill paying are a nightmare. Certainly some countries are better than others, are more integrated into the international financial infrastructure, but taking care of finances from a foreign country is an ongoing never-ending problem.
Western Europe is out of your league, it's so ridiculously expensive you can't possible afford to live there unless you're an independently wealthy American or a backpacker. There are issues with extended visas, permanent foreign residency, visa renewal, taxes....dealing with international government bureaucracy is not for the faint hearted or short tempered. And it has to be done every few months or every year, over and over again. At some considerable expense. Since you mentioned them, Australia and New Zealand are nearly impossible to immigrate to. And yes they do speak English (sort of).
That's just a thumbnail. I have more, plenty more. But easily the biggest issue is the language problem. I'll never forget the time I went to the cosmetics store (I'm always guessing as to what something is, the label is all in a foreign language and alphabet) and I finally bought what I was sure was face moisturizer. But when I put it on it felt weirdly waxy....so I took it to a bilingual native and asked what in the world it was--it turned out to be makeup remover.
Multiply that by anything and everything you buy. The smallest tasks and errands you take for granted in America can each be a huge struggle in a foreign country. Every day.
If I can help you with more specific questions, please ask.
P.S. I was in the UK last week, where they speak English (sort of) and it-was-the-most-expensive-place-I've-ever-seen. Ohmygod, the price of everything had to be doubled to convert to dollars. Stunningly, amazingly, stupendously, expensive. You won't be moving there.