I have to think the class sizes at Wesleyan and Vassar are pretty similar since they have identical student/faculty ratios (8:1.) Popular professors will tend to draw bigger crowds. One of the largest at Wesleyan, if not the largest, is taught by the president of the college and tips the scale at 90 people. Special efforts are made to get first-year students into seminar-size classes as quickly as possible through the First Year Seminars (FYS) initiative:
https://www.wesleyan.edu/academics/journey/fys.html
The arts are highly collaborative at Wesleyan, the best example being the filmmakers who depend on other students for everything from production assistants to actors, to musical scores. Theater is also very popular and there are faculty productions as well as student run productions; proscenium arch productions as well as black box. All are heavily attended.
I don’t think there is a core curriculum at any of the three colleges in the subject heading. Brown has a so-called “open curriculum” which basically leaves it to individual departments to decide what prerequisite courses are required for the major. Wesleyan adds the additional “expectation” that graduates have taken at least two courses from all three academic divisions (natural science and math; behavioral and social sciences; and art and humanities), but it isn’t strictly enforced unless you are vying for Honors.
At Vassar, the requirements in addition to the major are pretty minimal: Everyone must 1) take a freshman writing course, 2) take a quantitative reasoning course and, 3) either demonstrate proficiency in a foreign language or take one year in a foreign language.