(1) Do not do MD/JD. This does nothing for you. The paltry, vaguely-defined value it adds is easily outweighed by the additional cost and time of the second degree.
(2) An MD/DO degree, if you can get it, will objectively be a far better investment than the type of LS you'll be looking at w/ your stats. (Even if you get a 163.)
(3) You don't need any particular major, but you will need a
year each of Gen. Chem, Orgo, Physics, and Bio. A non-trivial number of schools require 1
semester of Calculus, and a rising number (including all FL public MSs) require 1
semester of Biochem.
(4) The MS admission process is driven by your BCPM (biology, chemistry, physics, math) GPA, which incorporates only those courses. The AO (all other) and comprehensive GPAs are distant seconds. There are a few easy courses you can sneak into this category (Astronomy, Ecology, and Neuroscience at most schools), but a lot of the easier "science-y sounding" courses like Nutrition and Psychology don't count. The AAMC has a document that outlines exactly which classes count for which GPA, and I think it is a highly under-utilized document for those looking to game the MS admission system.
(5) Because of (4), you will largely be judged on the basis of your performance in the courses listed in (3). What you'll need as a minimum BCPM to get in will vary based on (a) your MCAT score, and (b) your state of legal residence. (a) isn't nearly as big of a deal as you might imagine, as even with a top 5% MCAT you'd still need a ~3.2 BCPM to get in anywhere allopathic. (b) is probably just as important as (a), since OOS med school applicants are almost unheard of, and are usually
strictly capped.
(6) You can't take the MCAT until you've taken the courses in (3), as they are prereqs for the test (not technically, but you'll obviously perform poorly since that material is on the MCAT). You will have virtually no chance below a 28, and a 30 is a highly-advisable minimum for which to strive. For reference, the median score is always between 24-26 (and, accordingly, the median MS applicant doesn't get in... anywhere).
(7) Use
The Student Doctor Network for MS questions.
(8) Med school will take a few years, and
lots of legitimate hard work (these are not poli sci courses). You can get into law school right now... and so can every other recent college grad with mediocre grades and mediocre work ethic and mediocre standardized test scores. Think about that for a second, and think about how it plays out down the line w/r/t employment prospects for the respective fields.
(9) FWIW, I am a current law student at a school far better than where you'll be going w/ a 157/3.66 (not trying to be a dick; read on). I would kill to be in med school, for a variety of reasons, and I may still go (I hope to God I don't lose my resolve). Med school offers a lifetime of guaranteed middle-class employment, entrance into a helping profession, and is attainable to people who aren't naturally brilliant provided they are willing to work their asses off. Law school used to be the exact opposite--you didn't have to be the hardest worker, but you had to be smart--but now the "you have to be smart" requirement has fallen off.