Regarding the language tests - for Cantonese, it's fairly simple. You will neither need to speak (for classes) nor be able to learn it. The only Cantonese classes offered as a part of the university curriculum are two very basic level short courses (4h per week) that are taken mostly by the ABC/BBC exchange students looking for an easy A . Furthermore, there is a Cantonese-for-mandarin-speakers course, but I guess that would not work for you either. Other than that, there is only the CLC program that is _not_ part of the undergrad or postgrad curriculum, and you need to get through tons of red tape to get credit for it. It took me two years of my three year program and an angry letter to the head of the graduate school to join these classes, and even that was only possible because, as a research PG student, I was very flexible with my schedule.
For Putonghua, there are courses at all levels. Just sign up for different levels in the first two weeks and choose the module you feel suits you best.
Re transport - there is a red mini bus from Wan Chai to Tai Po that passes by the campus entrance on Tai Po road. Pretty quick, but not all that frequent.