What the infrasonic filter does is exclude the frequencies you cant hear, this is valuable for several reasons. The most important of em imo is that by excluding these frequencies from the output you will reduce the power your amp is wasting to play notes you dont even hear.

Low pass filters will filter out higher frequencies you dont want. By setting the knob at 150 means that you will be blocking any frequencies that fall above 150Hz. High pass works just the opposite.
Input sensitivity is just another way of wording 'gain'

Depends on the kind of music you listen to, the shape of your car, the type of subs and the type of enclosure you have. Thats why i posted earlier that u kinda have to tune it by ear. with the music u listen to playing. For example if u listen to a lot of hip hop/rap and ur box is ported and tuned to ~40hz you may want to stay close to that frequency to avoid unwanted noise.
Whereas if u listen to a lot of jazz and u have a sealed box, you want to hear every single note from the bass guitar so the frequency should be set pretty high, so it comes down to your own preferences.
Input sensitivity is normally a gate that regulates the input voltage that drives the amp at max output. So in this case, 5v is greater than 0.2v ofc. the higher the input voltage rises, the more noise you gain. This is hardly a problem with monoblocks tho. You can easily find out by turning the knob, if the volume goes up, ur increasing the input voltage.