smallbearsis: All residents are given the same 31 week contract (domestic and international) and everyone is given the option of paying extra to stay during the holidays (same weekly rate as during term time - the prices on lsevacations are for tourists). You can choose a few weeks before whether to stay during the holidays, just let reception know (if there is a royal wedding, you have to tell them well in advance, but given current circumstances that's highly unlikely). Hope that helps.
silent)123: Yeah, a lot of people who live in London decide to stay in halls for their first year just so that they can fully integrate into uni life. As for your third option, it depends what you are looking for! Bankside and Holborn are more expensive, but Holborn is closer to campus and Bankside is by the river. From what you say (about wanting to be involved in the social life), you should probably choose a hall with a corridor layout (Rosebery) rather than separate flats (Holborn).
englica: Good question, however unfortunately I don't know the answer! Sorry!