As long as you have Nottingham as your firm choice, and have applied by a certain date (I think it's 1st August, but you should check on the website) you are guaranteed to have some form of university arranged accommodation provided, but not necessarily your first choice. As far as I am aware, accommodation
is allocated on a first-come first-served basis. This year you can't choose which hall to go into, beyond which campus you want (either University Park or Jubilee). They're all basically the same - all have very similar facilities, and it's the people that make them anyway.
People go for both. There are about 4000 catered places (give or take) which are usually fairly full, and probably about the same number of first-year students go self catered. Just pick whichever you feel would suit you best.
There are always vegetarian options provided at mealtimes. They do cater to other dietary requirements too, as long as you give them advanced notice.
Depends. If you go for an en-suite, then no you don't have to share a toilet. Other room types, yes you will. It may be with one other person, or several. No room type is 'best', it just depends how much money you are prepared to pay, and how bothered you are by sharing.
See
this webpage.
You can if you want. The majority of people move out after first year, into privately rented accommodation.
If you want to stay in halls the following year, notices will go up shortly after Christmas advising you how/when to reapply. In all catered accommodation, you have to move everything out of your room at Christmas, Easter, and over the summer, as the university uses the rooms during those times. Some storage space is provided, but it is not guaranteed to be secure, and is prioritised towards international students. Self-catered accommodation requires you to move all your stuff out only over the summer, not at Christmas or Easter.