1) Just follow the instructions. They are straight forward and it is pretty hard to mess up an intake install.

2) Looks like something that the previous owner added that he removed. Those are available at any hardware store, so he must have tapped into the fuse box to power something.

3) That resets the maintenence required light. The box just holds odometer information that will cause the light to flash after driving for a certain amount of time reminding you to take the car in for maintenence.