If your school has a pre-med committee, they can probably do a better job answering these questions 🙂 And it may not even matter because some schools require EITHER X number of letters from science/non science OR a committee letter. If you're doing the latter, it's not as big a deal. At least, it didn't seem to matter that almost all my LORs were written by psychbio professors (ex: Behavioral Medicine). I'm doing alright in the process so far (8 interviews out of 18 applied), so I don't think it counted against me that a lot of my LOR writers weren't "hard" science professors, it probably mattered more that they wrote me strong letters 🙂 (I hope!)