All workable problems.
Humans, evolved for African savannah, survived the Ice Ages and thousands of years in the Arctic using only the most basic technologies.
An underground Mars civilization would do just fine. Same for the Moon, where I expect the technologies will be debugged before dealing with Mars.
If there is enough incentive, more work will be done on the medical issues of gravity and other things. Research on this kind of thing should be one of the top priorities of space station labs.
One of the questions I've always had is:
Would the biological changes of zero-G be a problem if a person decided never to return to a gravity field?