Yes, granite is very dense and durable. In most cases you will do no damage at all to your countertop. This will be discussed with the particular stone you choose. You will damage your knives with continued use on the granite.
No, in our experience quartz is a good product for the kitchen but special care needs to be given to keep it looking the way it was installed. Quartz can scratch easier than granite, and the manmade resin used in creating the quartz can burn or discolor if heat is applied to it.
It is very difficult to damage granite. If a chip occurs we are able to fill it with epoxy and polish it out, if a scratch occurs then a polish of the face will be in order and is easily done by our installers the next time they are in your particular area.
No, granite has pits, veins and voids. It is a natural stone out of the ground. No two pieces are exactly alike. These particular characteristics are to be pointed out to the client before choosing their particular stone.