It's been my observation that a MLS/MLIS degree is less often listed in the job requirements for a patent searcher position as opposed to, e.g., a position involving a broader scope of subject matter and resources, especially in academia. However, I've been told that many HR departments in larger firms make an MLS/MLIS a requirement to demonstrate searching experience for those really new to the field. For any searcher position, prior searching experience often carries equal or even more weight than the degree.
Not only do patent agents often become professional searchers but professional searchers often make the effort to become patent agents (and often continue to be professional searchers).
Professional Liability Insurance ("Omissions and Errors") may be a good idea if one can get the appropriate coverage for something other than a king's ransom. I've been informed that the opportunities are much better than they were 13 years ago (when I was becoming a professional searcher). For example, the ACS has reinstituted availability of professional liability insurance although I've seen no evaluations or comparisons. At a minimum, the new searcher should incorporate in some fashion (LLC, S Corporation, etc.) and of course, keep a separate set of books. For both functions, the engagement of a good accountant is usually sufficient and the advice of an attorney may not be necessary.