Okay, so I’m only going to speak to Grinnell and Vassar as I am a current freshman at Grinnell and one of my good friends chose Vassar. I know that in the two years she’s been there, it’s been difficult for her to get involved in theater because the theater there is very serious and hard to break in to if you are not a major. That being said, if you are super good at theater Vassar may be a great option for you. At Grinnell, things are very open. There are not as many theater majors, but that means students of all backgrounds come together to make theater happen here. I am an English/Economics major and I plan on acting and/or singing in a production next year. My roommate who is a physics major works on lights and sound. This makes theater here feel more like an extension of the community. Since there aren’t as many theater majors, they can be almost guaranteed a role in whatever production they are doing. You can do something called a MAP (mentored advanced project) here for credit for writing, producing, or something else. You could also gain credit for teaching a theater class to area middle school students. There are for credit opportunities in the college’s singing groups as well. If you have more questions, feel free to contact me personally. If you come to campus, I’d even be willing to give you a personalized tour. 
Finally, even if you’re remotely interested, apply to Grinnell. There’s no application fee or supplemental essays. 