1. You will need approximately 1.2A per meter to drive them at full brightness. This
would be a good choice to drive them.
2. The positive terminal goes to the '+' on the led strip. The negative terminal connects to the Arduino ground.
3. The MOSFET is your driver. The strip has the appropriate current limiting for a 12v supply built in.
4. To dim the strip, you just need to connect the MOSFET gate to one of the PWM pins (3, 5, 6, 9, 10, 11) as shown in the circuit diagram. Brightness is controlled in your code by calling "analogWrite()