Gut feelings are god. Trust your gut. Go with the gut. Although, if you're like me, you have to make sure the gut knows what it's talking about.
I bumped up another thread entitled "info websites" or something like that which has lots of websites you might find useful, including a page of one of the other posters on this forum.
In terms of preparing yourself, the best thing to do during the first couple of years of med school is to 1) learn the material and 2) start learning about different fields you might be interested in. During 3rd year you will get lots of exposure to the traditional fields. You don't really have to decide what specialty you want to pursue until a couple of months into your 4th year, although it helps to have a fairly good idea towards the end of the 3rd year so that you can start planning elective rotations and thinking about letters of reference, as well as programs to apply to!
I wouldn't worry about doing things to increase your chances for a residency, unless of course it is something (like an interesting research experience) that you yourself want to do. Don't do things just because they might look good on an application. The best ways to improve your chances at a successful match in pathology are doing well academically and demonstrating an interest in pathology. This can be through talking with faculty, perhaps getting involved in a research project, or doing electives. Electives don't really happen at most schools until 4th year but that is still early enough to decide.
There does exist at many med schools (some also take students from other schools that don't have one) the post-sophomore fellowship which I and others have done. You extend med school for a year and do pathology. Different programs run it differently. At some it is basically a glorified observership (and a year is a long time!) but at others you are given responsibility equivalent to resident level. PSF's are helpful for those who are somewhat undecided on the field they want to pursue. They are often used by people who are completely decided on pathology, and want to do the extra year to demonstrate their interest and perhaps improve their application. Programs are somewhat impressed by people who go through this year because it has demonstrated not only that you can be successful in the field (hopefully you will have LORs from this) but that you have completed a year of it and you know that is what you want to do. However, don't misinterpret me to say that only people who do PSFs or have an MD/phD will get good residency spots. Far from the truth. That is why I and others will tell you to only do a PSF if that is something you really want to do. Because, if you are only doing it to do pathology, you are going to have a future residency in front of you anyway, so doing an extra year just for the heck of it is a bit of overkill.
So, look at the sites. Some of them have advice for med students on things you can do. Others will explain the different areas of path better than any of us can. good luck...