Should you have a problem with your assigned housing, contact the London Director or the London Administrative Assistant for help. Yes, whether you go through USD or on your own before you arrive or when you arrive in London. USD would not be able to help you find housing OFF campus. It would depend on which type of housing you selected. It will vary, depending upon your landlord.
Landlords usually charge the first months rent for the deposit.
Yes, if you are staying off campus in an apartment . No, everything is usually provided. No, everything is usually provided or can be bought. If you are securing an apartment or a room with a family then probably yes. This will depend on the landlord, check with the landlord, but more than likely yes.