Hi bnhinparis!
I can answer some of your questions...it'll be a start anyway!
1- Most utilities arrive for payment or are debited from your account if you've set payment up that way, every quarter. More and more though, there are companies that offer monthly payments.
What I found very strange here is that no one comes to 'read the meter'....they just guess how much you may have used and then correct it later.
My hubby and his previous flatmates went for years without having a man by to read the meter since it was inside the house and they weren't home much during the day. The amount they were paying was seriously lower than what they were using.
2 - I'm not too sure about deposits. I know we did not have to make any deposits for utilities when we moved to our own flat here in London. I would say no, but better check with the providers to make absolutely sure.
3 - Estate agents won't laugh, don't worry! You can tell them you want a certain number of beds, bath's, and shower type. Large kitchens are pretty hard to find around here, but if you are prepared to pay for them, and I mean pay rather dearly for them, you'll be able to find them.
The only time an agent may chuckle is if you go to them asking for a two bedroom house/flat with more than one bathroom, large kitchen, and then set a low price limit.
London housing is exorbitant! Just be prepared to pay a lot of money for a small, but decent place, or be prepared to compromise on the less important things on your list.
Best of luck!