I think you may be over complicating this installation. If you search for Justin's threads, he has a detailed description of how to disable the aux fan and install an electric fan with a 2-speed motor. It's really, quite simple.
Along with this, you retain the system built into the car to start the fan when the conditions are properly met. Adding extra circuits and extra fuses is completely unnecessary.
Using Justin's write up, I am happy to say that I have had this conversion for the past year in Hawaii without a hickup. Granted, I put in a lower temp fan switch, but the fan comes on its self just after the 1/2 way mark - every time, using the wires and relays that are already built into the car.