Slate On Drywall Advice On Redoing My Fireplace - Want To Add A Mantle, New Stone Facing, And Cover The Chimney W/drywall?

Advice on redoing my fireplace - want to add a mantle, new stone facing, and cover the chimney w/drywall? - slate on drywall

I have a 2-storey vaulted ceiling in my living room. The present focus / chimney is not a coat and red brick was painted white. I would add a simple overcoat, some marble, slate or other rock wall below the layer and the brick fireplace on the ground.

About the coat, because the brick chimney is 20 meters, I would cover the fireplace with drywall to cover up the bricks and adds more depth to the wall. So my questions are:
- Are there any risks to the bricks and mortar to existing stone? In view of the brick is structural, not decorative, did not want to break.
- Are there problems in the brick above the mantle will soon be constructed with drywall? Not sure if you are making a home carepotential problems with heat or fire code.
- Any idea how much should it cost?

Thanks in advance!