So 2 gap years is what it''s looking like? Is that the norm these days? I'll see what I can do with the time I have left in UG as I'm not really going to graduate spring 18. I can do 12 with research but 16 credits and research seems like hell with upper div bio classes. The max I do is two tough classes and 2 less tough typically non-hard-science classes. So far I've been doing 16 and 17 unit semesters. I don't think they really care if you do 12, do they? I know plenty of people who take 12 units to focus on certain classes that got in pharmacy, podiatry, and other professional schools.
I'm not sure what the norm is these days. But you should be able to work EC's and MCAT studying into your undergrad. There's no reason to wait. I think every pre-med should commit to 5-10 hrs of volunteering/research per week, year-round, the minute they decide to pursue medicine.
The best way to study for the MCAT is actually to take the pre-reqs (ideally as concurrently as possible), get all A's in them (studying for pre-req = studying for MCAT), and take the MCAT a few weeks after the year ends. That's exactly what I did--I took gen chem over the summer, followed by bio/o-chem/calc-based physics over the school year, did ExamKrackers books (didn't finish any of them or their question books, but I went through a decent amount) + AAMC practice tests (I did take all of them) over about 3-4 weeks when the year ended, then took the MCAT.
You really don't need upper-div courses to do well. The MCAT is designed to test knowledge from your pre-reqs, and people tend to forget a lot of that basic stuff if they wait a few years. I didn't do any formal review course or take any upper div science courses, and managed an MCAT that opened the doors to every school in the country. (My cumulative GPA didn't though, so I didn't bother applying to the Stanfords and Harvards out there...)
I think if you take a lighter courseload you have to be prepared to answer why. It's fairly common to take full courseloads (which can differ by major), so med schools may question if you can handle the rigors of med school. I'm sure if it's just one semester/quarter they
probably (don't take my word--I'm not an adcom) could care less, though you should still be prepared to defend your rationale.
Still, a 12 unit courseload where you get a 4.0 is obviously better than 18 units at a 3.5, so I'm not trying to say you have to take a full courseload. You have to do what's right and best for you.
Odds are if you can't commit to 5-10hrs a week in volunteering/research right now, you are probably not studying efficiently. If that's the case, try meeting with your academic advisor/counseling center to go over your study methods. It's best to get your study habits perfected now.
Don't make the mistake of thinking that just because you work really hard and get good grades now that what you're doing is the best way to study. I know it's annoying to hear people say "study smart, not hard," but it's true. I learned that feeling like you're studying and putting in effort is very different than actually studying. You have to figure out which methods actually help you learn--for me it's drawing things out and talking them through with other people.