I'll try and answer your questions as best I can for you...
The front of the engine, what you see is the 'fan', as said earlier, it's a freewheeling one that is connected via cocentric shafts to a couple of turbine wheels at the rear of the engine, and they also turn with the fan, though as a passenger you won't be able to see that far up into the rear of the engine. This fan arrangement is simply being spun by the prevailing wind, either forwards or backwards, it doesn't matter, the core engine will start to rotate the fan in the correct direction during engine start.
Again, as mentioned, the additional noise you can hear during boarding, and right up to just after engine start is the APU, which is the auxiliary power unit, on most aircraft it's located in the tail section and provides both electrical power and pneumatic power until the main engines are started. The allows for electrically powering up the entire airplane and running the air cycle airconditioning systems. The pneumatic power is also used to drive air motors to start the main engines...except in the new Boeing 787 Dreamliner, where this job is done with electric starter motors.
The last question has already been answered...
Cheers EW73