Hi Mates,
I would suggest the airhorn is a priority for most riders, I fitted one and it has been a fantastic addition to my bike and stopped numerous idiots trying to move into my space eh!, as for the fan I would agree that it would be a good thing to run your bike cooler though I have fitted Xied's to my roadking and that has dropped the engine temp quite well though probabley not the same thing as a mechanical device though.
Regards Len