You're taking just the right approach, asking the right questions with years to get everything right. Good job.
In addition to the above, read Planet Law School, which has quite a bit in terms of getting ready, and, if I might, my own book Law School: Getting In, Getting Good, Getting the Gold, which takes a more moderate approach.
In terms of an internship, this is also an excellent approach. There are two possibilities: finding a job in a firm or law office, usually as an assistant, secretary, or even office runner, or volunteering at an organization of interest. In the latter, you'll likely have much greater opportunity to see the real world of law practice, but of course these are often unpaid. Even so, these are well worth it. A note of caution: these are great for answering some of the basic questions, and in getting valuable professional feedback and references, but be careful in not putting too much of this in your law school applications (for reasons explained in the latter book above).