Mic basics. You want your gain set as high as possible without distorting. As long as you have no distortion, you can clean up the rest in post processing. You shouldn't need to do any keyframe adjustments if you become familiar with audio compression. A good starting point is to set all of your dials and sliders at 50%. So in windows, set the mic recording volume to half, set your gain knob to 12 o'clock. And adjust from there. If it's too high already, turn them both down slightly. What you don't want is the windows volume at max while the gain knob on your mic still hasn't left single digits.
Fans are always a problem. Don't block the fans but put something between them and the mic. Large sheet of cardboard maybe.
Noise reduction doesn't work very well on clicks or breathing. It's purpose is to remove ambient noise, not active. So the steady hum of the furnace, the sound of a fan, etc. These are consistent noises that you can grab the pattern of and remove to some degree. Breathing will be a different sound signature every time, so it won't remove well. Recording some silence at the beginning just ensures that you have a pure section of nothing but ambient noise to sample for removal.