another recommendation question

I'm actually planning to apply to an Alternate Entry MSN program. I need three references for the grad school (which was also be read by the nusing program folks). I have history instructors who can comment on my graduate ability, nursing pre-req instructors who can comment on my scientific potential, employers who can comment on my work ethic/moral character. I am also going to start volunteering at a hospital and will have a potential reference there. The trouble is limiting it to three---I could really have six or seven. Which do you think would be the most advantageous for me. Definitely one that can comment on graduate potential---but do you think nursing programs would want a reference from instructors in pre-reqs or are they only interested in grades in those courses. Or would those references be better spent on moral character and/or work ethic?