i'm using some steel pin points i find they help focus everything better then the sorbothane I have also tried. seems everything I used that isolated softened the presentation the hard points tighten everything up and adds to the detail.
I have a custom 301 with high density compressed bamboo ply / birch ply hybrid plinth I built myself. I have also put together a 301 with double layer high density compressed bamboo ply and a 401 with engineered stone plinth for friends.
I prefer rigid feet to ground the TT. The only exception I have found if you have feedback is the Isoacoustics footers (trialled on a 401/Kuzma 4point combo ).
I use only 3 feet asymmetrically placed to ensure the motor and tonearm centre of gravity are within the triangle - 1 to the centre left of the motor. 1 behind the arm & 1 on the right front. 3 feet always sounds better than 4.
Personally I am not a fan of granite - have tried it over the years in various applications and to my ears always seems to add a resonance ( ring ) - high mass does ameliorate this but it is still there.