I am going to London with my girlfriend in 14 of February we will stay in Kensington for 6 days.

So any suggestions? Forget those obvious places to go, i want stuff that tourists usually don't see.

1) Any good restaurant? Cheap one... 14 is valantines day so i was thinking in some romantic place for dinner.
2) a nice park to give a walk
3) anyone knows what is the best spot to take a picture of Pink Floyd Battersea Power Station?
How do i get there? Should i go to Sloane Square metro station and cross the bridge?
4) i read about the London pass and the Oyster card, can i buy them in any tube station?
5) Best way (cheap) to go from Heathrow Airport to center of London? Train? Cab? Tram? Bus?

6) And major question, can anyone explain me the "changing of the guard" i always thought that it was only in one place, but i saw that there are 2 and also horse parade/change guard or whatever it is. But some sites point almost 10 places where changing guards occurs.... i am confused... where is the main one? Is it true that we need to be there 1 hour before to get a spot?

7) what are the areas that i should avoid related to safety at night? Center only areas 1 and 2, i should not go beyond those areas...

Thanks