granite backsplash installation

I am putting in granite backsplash and my contractor remove the tile backsplash off my wall and have made many big holes in the drywall. There are parts where it is empty hole. Does the hole need to be patch up, and with what before the granite backsplash go on? Please help. ASAP

The drywall should be removed and totally replaced. Yes the holes must be patched so as to accommodate the grout at the very least.

Granite tile or one large piece cut to fit?

If tile, what Bud said.