Not as a standard rule, it depends on the song. Even if humans don't hear below 20hz, those frequencies move in the air and bring energy, you don't hear them but can feel them. Expaecially with big sound systems. It also depends on where the fundamental and rumble of your kick are, and on the genre as well. I prefer to do those cuts during mixing individually on the instruments/groups that need it.

I usually go through my “important” elements and cut until I start losing the “full” sound usually I end up cutting most by 90, except for obviously my kick and sub elements

Considering that a rolloff filter will always create some resonance around the center frequency, I would only do such a thing with a gentle curve, not a steep one like what’s shown here. And I could totally see value in a gentle dip down there for some tracks.

Not everything. Only cut what you don't need down there. Only a few instruments extend that low, and if they aren't adding anything nice, just rumble and noise, masking and muddying other things in the mix like bass 808s, kicks, etc., then cut them out. I always prefer to use a low-shelf though. Sounds better in my opinion than HPF.

Depends on what SPAN says how much and If i Cut some stuff

Bro nothing there