1) Regarding the entrance exam preparation, if you're from UK, then the exam is tested on all A-level stuff. If you're from the US, then it's tested from the AP level courses. I would recommend that you review all the topics (mentioned on the syllabus) or get a UK A levels books and review from that.
2) Yes, you can transfer if your Czech is good but Czech isn't really an easy language to master (I'm trying so hard and this language just gets harder and harder...with 7 grammatical cases, 2 verb pairs, and the vastness of the vocab.). Unless you've taken some advanced immersion course for 10 months or so, it's really not that easy to transfer. But of course you get a few advantage when you transfer like the fact that you have to pay a very minimal tuition fee. But it can also be very ruthless in the Czech parallel......they're very strict and even if you don't get your semesters' credit, you're out...as opposed to the English parallel where they give you an entire year to get your semester credits.
3) The student expenses vary from person to person so I don't know what exactly is the average. But from what I've seen and heard, it's anywhere from 500 EUR - 750 EUR. I'm sure you can manage at a lower range but then you would have to compromise on a lot of things (like living in the dormitories n stuff).