As far as cutting a hole in the granite, I would contact a local cabinet maker, installer. They should have the tools to make the hole. They can also advise you on how to fasten the tower. My guess would be to glue in on with something like PL-500.
Keeping the lines cold is easy. Find a cardboard tube about 3-4 inches in diameter. Make sure it is strong. (like a concrete form) Punch a small hole (1/4 inch or so) in the side of the tube. After the lines have been run thru the tube and everything is ready to go, place the tip of a can of expanding foam insulation into the hole and fill. Be very careful when doing this. The foam has a tremendous expansion and can rupture the tube or squeeze off your beer supply line. I would make a second tube and practice with it before filling the tube on the kegerator. Good luck.