My uncle's a doctor, and he's certainly comfortably well-off. I think it probably varies quite a bit by country. The cost of living here is pretty low, for instance.
There's a difference between being comfortable and being wealthy. Also, I emphasize once again: WORK HOURS. Back when I was a resident I was earning more than any other of my former high school companions or same-age relatives. I was also putting in around twice or thrice as many hours per week as them.
I'd add that it probably varies the most by specialization and level of specialization.
Less than you might think. There are some differences by the type of contract, rather than the level of specialization (there aren't many levels to begin with. In many places there are only two levels). There's some difference between specializations, but once again it mostly comes down to WORK HOURS. If you're working more hours you earn more, even if you're not earning all that much per hour.
If you check Medscape US statistics, several surgical specialities are paradoxically both amid the "best paid" ones and amid the "least satisfaction" ones. In contrast pathologists don't earn all that much, and paradoxically are more satisfied. Why? Work-hours.
Ability to arrange a business all-by-yourself is there somewhere, but in most cases it's basically adding more work-hours to work-hours. Far less profittable than people think.
Not if it means they can hike up the costs of treatments because of it.
Yeah. Because doctors are totally the ones setting up the cost of treatments.