re: At which salary level is an individual “doing well”?

There's a sliding scale.

Where I live now, I don't see how you can even exist without a household income of $125-150k or more. Median housing prices are over $789k, and private schools are $15-25k. There's a tax or license or fee for every damn thing, and I think they even tax our tax. I can't cut down a tree without a permit and canopy analysis.

Where I am from, you would live like a king on $50k. You can buy houses with acreage for under $20k. You can build a NEW 3br house with acreage for $100-125k. You can buy a dang lakefront house for under $300k, and if you want a trailer or shack on that lake lot, you could be in for $50 or less. Private schools are $5k. You can cut down all the damn trees you like.

*edited to add, I went to visit a guy that was on my team at my last company for a "retirement" party, since the company isn't doing one for him. Dude is 60 years old, never made more than $70k, and is a multi-millionaire. Of course, he never got married and has no kids, and doesn't live an extravagant life... but he is an avid investor, and has been doing so since he was 18. I call him for tips from time to time. His brother is about the same age and will retire this year, too.