1. You'd need to let your university know and probably do a little bit of paperwork
2. You will be liable for a part of this year's tution fees. As far as I aware, Student Finance will provide you funding for the intended duration of your course plus a "gift year". If you're in year 1, then this would count as your "gift year" and you should still be technically eligible for tuition fee and maintenance loan support. However, you're better off asking student finance themselves.
3. Yes, you'd need to declare it on the education section of UCAS and yes, you'll need a reference from your current university if you wish to apply to uni again
4. Generally, it is possible to switch uni or course, although it really depends on the uni or the course you wish to switch to. But broadly speaking, yes, it's a possibility!
5. It depends on the university, although I think in most cases it shouldn't affect your eligibility for accomodation.