Re getting around the Five Colleges (Amherst, Hampshire, Mount Holyoke, Smith, UMass), there are (no charge) buses continuously circulating among them. Attending classes and events at each institution is easy.
This is the webpage for links to programs and auditions among the five schools:
https://www.fivecolleges.edu/theater
https://www.fivecolleges.edu/theater/auditions
Oberlin has a strong vocal performance major and a separate theatre program; my recollection is Oberlin does not put on musicals… rather, it puts on concerts, plays, etc.
LACs that I know of that put on musicals are Wagner College (does up to four mainstage shows) and Muhlenberg College (at least one mainstage show during the year and three during the summer).
http://wagner.edu/theatre/wagner-college-theatre-announces-season/