He will give you facts and recommendations, and that's it. Lawyers dispute whether you need independent counsel for investigations. Much depends on maintaining the lawyer-client privilege. Once any fragment, no matter how small, is gone, the whole privilege is history. Judges can require your lawyer to testify about your secrets.
Good investigators look for information in various places.
Talking to Buckbuster and Beanman won't do the trick, although both must be interviewed up front. Sexual harassment, however, almost never takes place in front of others. The assignment requires Outstand to decide credibility by talking to others and going through documents and seeking corroboration. He will want to know whether anyone saw Beanman's misdeeds. He will want to know whether Buckbuster told her friends about her problem.