Having never used anything beyond Linux, Windows and Mac, what would be a good starting point? Can I expect gnu/coreutils to work as is (ls, cd, pwd, et al.). Can I expect to not get bitten by arbitrary issues? What if one of the emacs packages that I am accustomed to using doesn't work there due to a dependency on something that is Linux only? How likely/possible is that?
> Having never used anything beyond Linux, Windows and Mac, what would be a good starting point?
GhostBSD.
Without looking or knowing all your requirements, it's likely everything you need works the same. (I don't know anything about gnu/coreutils.)
All the utilities are not GNU, but BSD, so there are differences. But typically not a problem, as long as you move inside POSIX. Most GNU utilities (all?) can be installed if you prefer them. For example, make is typically gmake, and you really need it. I haven't used BSD for the last 10 years but used it from 1999 to 2015. I had never major issues.