I am currently finishing up (i.e. in the data collection part of my dissertation) a BS to PhD. I went straight from my BSN to my PhD (well, I had 9 months of full-time work between an accelerated bachelor's program and starting my PhD program), BUT, I also was a returning student with a lot of life experience.
That said, my program has had everything from people like me, to people who had been working for quite a while, to people who were in their 20's and had little experience. All have had at least some experience in either research or heath care (even if it was in a CNA or volunteer role).
What I have observed* is:
If you are going directly into a PhD program post receiving your BSN, it is essential that you work at least part-time. You cannot develop the deep thinking about nursing and clinical issues without clinical experience. I see that that is your plan, and that shows good thinking.
People with limited experience, tend to have a harder time deciding on a research topic -- not a general area, such as you have expressed, but the specific topic that will become their dissertation. That said, I think it is also important to be open, as you go through the early years of a PhD program to ideas other than the ones you come in with -- your learning and understanding will grow as you progress through the program.
As BBFRN stated, you need to look for a program that has faculty doing research in your area of interest. That said, it could be people doing work on MH issues, people doing work on health disparities...possibly even policy-focused research, but that's a bit more vauge.
Once you have found institutions with like-minded faculty, interview the school -- talk to potential mentors/advisors, talk to current students, find out how they structure their BS to PhD program, who their students are, how they support them etc. If you are interested in teaching as well as research, I would also take a hard look at the curricurlum -- do they include classes, or access to classes about education? As someone with limited nursing experience, you will have an harder time making the transition to the classroom w/o some education background.
One thing I would NOT suggest (and I admit, this is my bias showing) is a distance learning program. I think they are difficult for anyone, because you do not get the socialization or informal time with faculty and colleages, but particularly as a new grad with little experience, I think you need to potentially supportive environment of a campus-based program.
One last comment, which is not meant to discourage you: something that has become evident to me as I go through my program and watch others in their process is that a PhD is not for everyone. Be open to finding out what does and doesn't work for you, and do not become so stuck on a particular vision that you loose sight of what is really the best fit for you.
Good luck with your decisions!
*anecdotal, not empirical evidence