Lowe's sells granite adhesive,
get this stuff, it will not let go without having to break the sink apart. I used it to set my quartz counter tops, within 5 minutes I could not pick them up anymore off the cabinet.
I will highly suggest you do any and all polishing outside before bringing anything inside. You only want to make the final seam inside. Cut it with a diamond blade and preferably water on the cut. I got
THIS polisher from Amazon and it worked great for my house, and two others have used it for their places also and it is still chugging along.
Amazon also sells the
two part epoxy and
coloring to seam the tops together, as well as the
Clamps to make sure that they are perfectly aligned.