[trekkor]

On the sandpaper, you will go through a lot of discs.

They make sanding discs that are made of resin with industrial grade diamonds in them. I have a complete set. 50 grit all the way to 3000 grit.
They are about $40 each and are used wet. You acn polish granite with them.

Just get a "contractor pack" of 80, 120, 240 and 400 grit papers.
Use the 80 grit until all the saw marks are gone. Then move to the next paper. 120 may be enough for you. You'll have to try a sample area.
The installers really should be handling this.

The splitting of the stone surface. I call it "shaling". Use a putty knife, margin trowel or a strong jet of water to clear the loose surfaces.

Your installer should have done that too.


KT