Jfrech!
Nice system. I´ve heard (rumours) that hard slate is even better than granite in absorbing energy.
Having a heavy platform in either granite or slate on a stand will make it less sensitive towards footsteps and vibration in general. Differences in absorbing, and rejecting, various frequency spektra varies with type of stone/composition.
I have TW Acustic Raven One turntable with SME V and AirTight PC-1 cartridge. A non-suspended turntable whereas
SME20A is suspended. I´m not shure wether it will make more or less difference with a heavy platform underneath a suspended turntable. Only way to find is to try, granite is no that expensive, make shure surfaces are flat especially using Cera Puchs.
Regards and enjoy music!