A: Yes these can be applied over existing tiles.
A: They are vinyl so putting them around a fireplace probably isn't a good idea.
A: Yes, you can paint them.
A: We do not recommend painting them.
A: They are glossy vinyl. Paint probably won’t stick.
A: These come in packages, not boxes. There are 4 tiles that are 10-1/2 inches by 10-1/2 inches square per pack (see description), so you will need 2 tiles for height and 4 tiles for length, or 8 tiles altogether, so 2 packs are needed to cover an area 36 inches long by 16 inches high. It goes without saying, you will have to do a bit of trimming to even your sides/edges.
A: You would need 2 boxes (packs) to cover this area
A: Hello, You would need atleast 2 packages