Oh, yeah, you need to put that fan fuse back in
The reason you're hearing the fan come on with the defroster is because the A/C engages.
But you definitely want it available for cooling. Either that or you have to watch it like a hawk and run the heater blower (on hot, and on high) to bring the coolant temp down. But in either case you're adding electrical load to the engine and cooling system, so you may as well put the fuse back in and let the car handle things automatically.
When the engine gets that hot, the computer is probably retarding timing, so in addition to going "in the red" and the associated risks to the engine/cooling system you're probably also losing efficiency.
Also, for better aero, I'd suggest blocking your upper grille and opening a portion of the lower one instead of vice versa.
I think it's safe to say there's probably nothing wrong with the water pump.