I use thinset mortar when setting ceramic tiles, but now I'd like to set some 12" by 12" stone tiles on a counter top. I saw "Marble & Granite Fortified Premium Mortar" at the local home center. Should I use this instead of thinset for the stone? I also have smaller ceramic tiles to set on the bathtub surround; can I use the marble & granite mortar for that or should I buy thinset?

I wanted to put granite tile over my brick fireplace
1. Should I put a wire mesh to hold the granite?
2. What type of adhesive should I use, my main concern is the granite tile is so heavy, would it slide down.
3. should the adhesive be heat resistant ....Thanks