We just had this done to our existing 5'-7" wide X 9'-2" tall brick fireplace. We used cultured river rock and a solid piece of blue stone for the hearth and two cobble stones to make a support for the mantle. The stone was applied directly to the brick, you should be able to add a mantle and hooks while its being installed. It took our mason 3 days to complete, and it looks great.

Cultured stone and other natural stone tiles (travertine, marble, granite, etc.) are typically applied using a fortified thinset mortar which bonds very well to unpainted brick. So it's pretty easy to install it over your existing brick. There's nothing wrong with installing a picture hook using a screw into the mortar so long as they used the right anchor. It's easy to install it into any new surface also by drilling and using an anchor.

Thanks for your replies. My fireplace is about 6ft 2in wide by 8 ft high.
Any idea on price differences for tile vs cultured stone? Are some surfaces less labor intensive to install, which would hopefully decrease $ amount spent.
Also what thickness is the tile or stone. I am wondering about how the insert will adjust to an extra layer over the brick. The insert sticks out with 3 sides, sort of like a bay window.