The best way is to install a backer board onto the cement using Tapcon Cement screws. 1/2 plywood or OSB would work then screw the NextStone panels onto the backer board.
Yes absolutely, NextStone is a non-flammable product! For a gas or electric insert, the NextStone can installed directly up to the metal frame. For an open wood burning fireplace, it is recommended to install NextStone with a minimum of 6 inches from the opening.
Unfortunately the Slatestone panels which are 8.25" high are a different profile from the Appalachian Gray which is the Country Ledgestone panels.
NextStone can be installed onto any solid substrate including Stucco. For stucco, cement screws are the best bet.
The manufacturers website (nextstone.com) does have a list of installers.
Yes NextStone is lightweight and can be installed on an interior wall
R Value for NextStone is 4.5 per inch of thickness
Unfortunately the Column Wraps are finger jointed and have a different interlock than the panels. An option would be to cut off the finger joints and straight cut the panels and butt them up to each other. This will create a seam that can be concealed with NextStone Grout and painted over with NextStone touch up paint.
The NextStone product is a solid polyurethane so it will not be easy for small forceful hail to go through such as vinyl siding. However, larger size hail stones such as golf ball size and up may create surface damage to the finish that can ultimately be touched up.
Unfortunately the NextStone panels can not bend. They would have to be cut at the angle of the radius and mitered.