What should guide my course selection for my 2L and 3L years?
Certain courses will prepare you for jobs in a variety of fields - litigation skills, trial advocacy, etc. Beyond these, I would select the courses that most interest you. This interest may turn into a passion for and expertise in a certain area of law, or it may convince you that your interest was misplaced.
Very few areas of practice require intensive preparation at the law school level. Law school is best at teaching you to think like a lawyer and giving you the tools to educate yourself in the law. Real practice is going to teach you what you need to know for a specific field. I have been doing primarily bankruptcy law for almost 15 years, and never took a bankruptcy course in law school.