A lot! Anywhere from about 700 - 1000 lbs.
you use a bbrush and you clean off all the dust on the cloth
The large main surface of a pool table. Slate is a stone, so it can be cut extremely flat and does not warp. I believe only expensive pool tables use slate, others use a wood product.
Depends on the make it is. Mine is a 7ft and is not slate.
Most billiard mechanics use beewax or a water putter.