Bourne shell is a predecessor of bash. Bash is the old Bourne shell having gone through the GNU treatment, adding lots of functionality.
I use bash consistently on all machines, even FreeBSD. Why? Because for shell scripts, the old bourne shell is much better than (t)csh. And I want the language in which I write shells scripts to be the same that I use at the command line everyday, so I am and stay familiar with the syntax (old joke, beware of the man who has only one gun, because he knows how to use it). For shell scripts, I usually go back to using /bin/sh (which is a subset of bash), and trying to use only features that were in V7 standard sh, but interactively, I enjoy the modern features of bash too much (even though I don't them in scripts). Ideally, I could use ksh or zsh or any of the myriad other extensions of the Bourne shell (all of the best ones seem to be derived form the Korn shell these days), but bash is trivially present on all machines I use at work, without having to do any installs there, and at work I use lots of computers, so installing something there would be a BIG hassle.
So, is it a good idea to use bash on FreeBSD? Probably not, because it is non-base optional software. For me, the benefits outweigh the negatives. Other people may not want to follow my example.
And then I go even one step further, and do something that I explicitly recommend people NOT do: I change the default shell of root on my FreeBSD machines to also be bash! I always create a toor account that has tcsh, for emergencies. I know that this will bite me one of these days, but I know how to get out of that pickle if I need to.
I think your choice of zsh is perfectly sensible, but that's really a personal choice. Just make sure you have an account like toor that uses a shell that ships in the base system, in case everything comes apart at the seams.