Hi Happycanuck,
I have been in almost the same situation like you. If everything goes well, I will receive my diploma in this summer from them though. Although there were some hiccups along the way, I found that it was quite doable. Most of my classmates were locals except for one girl who attended international school and did not know how to read Chinese either. If you are an ABC, BBC etc. and you have a reasonable grasp of spoken Chinese, it should not be much of a problem, I think. Besides, the competition to get enrolled into HKU is very high with everyone who doesn't speak Chinese trying to enroll, thus CUHK isn't such a bad choice.
Although English isn't my first language, just like you, my understanding of Chinese is mostly limited to an oral grasp of the language. Actually the only course that was conducted in English was the course specifically about 'Teaching English'. All other courses were in Cantonese (and one was even in Mandarin). On top of that, some lectures didn't have English notes (Hopefully you have someone at hand willing to do some translation work at times).
Having said that, you can attend the first few lectures of a subject that you plan to choose, and decide for yourself whether you think you will be able to manage that course. Some lecturers have notes and a style of teaching which are more suitable for English speakers. Most probably you will be doing the 'English language teaching' subject in the first term. I started a WhatsApp group with everyone from that course, and these contacts came in very helpful at a later stage of my study (I even owed a job to one of my classmates). Besides, I told all lecturers of the courses that I attended that my Chinese wasn't that good, and most of them were pretty understanding and sometimes willing to integrate some English in their lessons.
Good luck!