Have you looked at RID's web site about the path to becoming a professional interpreter?
From my personal experience I strongly recommend you attend a college that offers an ITP (Interpreter Training Program). Just learning ASL on the outside isn't enough. There's a lot more to the interpreting process and profession than just ASL fluency.
I don't see any reason to take sociology as a major. A broad, well-rounded education will be more useful to you as an interpreter. As a terp, your clients will expect you to know at least something about everything. You'll never know what topic might be covered in an assignment. If you're going to be a community interpreter, that's especially true.
Unless you live in a big city with a large Deaf population you probably won't find too many hospitals that have a full-time interpreter on staff. If you want to specialize in legal interpreting (which requires additional credentialing), that is an area that needs more terps.
If you want to be an educational terp, there are two basic divisions in that field. The K-12 division means you will probably be an interpreter/aide/tutor/babysitter combo, depending on the grade and school. (At least you won't be required to drive the little yellow bus like terps in the past did.) The other division is the college setting in which you'll be strictly in an interpreter role.
As far as "government" interpreter that depends on to which agency you're assigned. It could mean interpreting staff meetings, employee training, employer-employee disciplinary confrontations, or tour guide. It could include social services, IRS, military, contractors or a multitude of settings.
Then, there are terps who work in VRS, and who knows what someone from any place in the country might want to discuss on the phone. Be prepared!
As you can see, that's why you need to know "everything." I know that's an unrealistic expectation but that's the way your clients see it.
Even if you decide to specialize, I recommend doing at least a period of community interpreting to get to know a variety of people within the Deaf demographic, and to be familiar with the variety of situations they encounter. It will make you a better terp no matter what you decide to specialize in later.
