I definitely expect it to be difficult to find a seat. If I thought it would be easy, I'd probably have jumped in instead of really taking the time to think it through and ask questions. I'm not sure where all I will apply (or even if I will apply - I'm still in the very early stages of even thinking about this). That's going to depend on a lot more than just me - I've got a husband and three small children, so there's more to consider than "apply to every school in the country and go to whichever offers a spot." I don't see it going well if I get a spot in a place where my husband can't work and/or we don't have anyone to help with the kids. So there is zero point in my applying to a bunch of schools where I wouldn't accept a seat.
Also, I didn't suggest (or at least, I didn't MEAN to suggest) that I would use a first semester to test the waters. What I recall saying is that, should I end up at the University of [Where My Husband Can't Find a Job and I Can't Find a Babysitter to Watch My Kids while I'm Doing Rotations At All Hours], it would be really nice if I at least liked med school. Whereas, if I am lucky enough to get into my first choice of school, in a place where my husband already has his dream job, and we have a support system to pick up my family-duties slack, if it turns out that I'm miserable (as I expect many med students are at some point), at least I won't also have to deal with massive amounts of guilt from having screwed up life for everyone in my family, not just myself. I don't think it's wrong of me to consider that, in the worst case scenario, my local school would still be the best of several potentially bad situations.
P.S. I can only wish that my law school had inflated grades. I'd have paid extra for that handy feature.
I also had some strict limitations on where I could go, geographically. So, I applied to just a couple of schools, and I didn't finish the application for the 2nd one when it was clear that I was going to get into the one I wanted. There are a lot of people who would tell you that doing that was, at best, a ridiculous gamble and probably unforgivably foolish.
The reason it worked is that my stats were exceptional for the school I had chosen, and my EC's and clinical background would have made a strong case for me at any school. The narrower your applications, the more desirable an applicant you will need to be.
Study hard in those science courses, get a tutor early if you need one, and be sure that you are mastering the concepts. I took my basic science pre-reqs with an outline of the topics tested on the MCAT ready at hand. As we moved through the courses, I annotated that outline, being certain that I understood and could apply each topic. Don't take the test until you are ready, and give it your best shot the first time you take it. Scores aren't everything, but the higher the score, the better your options are likely to be.
When you do apply, have your application completely ready to submit at 9am on day one of the application cycle. That isn't really an exaggeration. The sooner you submit it, the more quickly it gets through the verification process and goes out to the schools, the more seats will still be available when schools start scheduling interviews. The prevailing wisdom around SDN is that if adcoms have 95% of their seats to give away, they can afford to be more generous with them than when they get down to 50% or fewer seats open.
It is wise not to bother applying to schools that you wouldn't consider attending... but as you make your school list, try to give yourself as many options as possible. If there is any school that you WOULD be happy to attend, if that were the only way you would get to go, at least include them on your primary application. It is always nice to have options.