Hi gumbikim, I visited UW last week and got to meet some of the current china studies students. They showed me what they are working on in language class. If you got an 8 on the HSK, I'd say you should probably be able to test into Chinese 4 with some reviewing over the summer. I study with the HSK advanced book and have some grammar difficulties, but I could read and understand the assignment the guy in Chinese 4 showed me. They will have placement exams when you go. Of course, brushing up over the summer will be helpful.
As to your questions about how it is taught in US institutions, classes are usually taught in English at lower levels, which I personally think places the students at a disadvantage in terms of speaking. As you progress, classes are taught more in Mandarin. But, if I were you, and what I plan to do, is to work on my reading. Try reading books, scholarly articles, the newspaper and things like that in Chinese. Also, if you can't already read traditional characters, you might want to start working on that. But honestly, with you passing HSK 8, I think you'll be fine!