you go to the happy mask shop in the market
No, you don't meet a keaton in the main story line of the game at all, but you can make them appear by summoning them with the keaton mask while standing where there are moving shrubs.
No, sadly. But there is a mask (in Majora's Mask) that looks like pikachu. It's called the Keaton mask.
If you've completed every step in the Kafei & Anju sidequest up to this point, talk to the Curiosity Shop Man in the Backroom at 1pm on the 3rd Day. He will give you the Keaton Mask.
Yes
Project64
They are at Gerudo Valley to the west of Hirule Field.
yes There is the origional for the GameCube and Ocarina of Time 3D for the 3DS
You can't, unless you hack the game.
To get the water tunic you have to find or buy it.
they are found in the spirit temple
You never kill Zelda.
You get them in the middle of the Shadow Temple as Adult Link.