any thoughts on building out the entire wall? Making that whole wall a statement?

If you took a photo back a bit to include the adjoing wall and the ceiling, even seeing your decor style with the entire room. LOVE the art!!!

Here's a couple ideas.

Custom Steel Mantel Surround

Custom Steel Mantel Surround with Black Framed Screen and Pewter Labyrinth Pattern Insert along with Modern Andirons. This hides the insert when not in use (which is most of the time). You would set the screen and andirons aside when using the insert, or store them during the winter if you plan on using the insert often.

Mockups Provided by: Hansen Wholesale

We provide these materials.

the baseboard would look weird.

since you've already done a hearth, continue your tile up and around the insert

Or just do 1 or 2 rows of tile up and underneath. on top, do a wood mantle like this.

all the squares would continue all around.

changed out the hearth to a solid black. gave you an oak mantle, diff decor. (I do like your art though). wish I could see what's off to the right

This after shot kind of reminds me of your style. See how they did the black surround, even right above the hearth? This is all you have to do. I love the vertical shiplap too

you could look for a diff insert. one that has the black that goes down to the floor

black surround that comes up underneath the box

You could use a deep, black basalt tile, cut it, and frame out the box.

or something like this, but the hearth would have to go

I would do any one of the last three pictures that Beth posted. The black surround, the basalt frame or the framing it with the white trim. The all black and basalt seems to fit with your decor best.

I am confused is this wood burning or gas ? The amount of fireproof materila around a wood burning FP is decided by the FP design and install. I agree probably the same tile as the hearth for a surround including the area below the firebox.I ahve no idea about your decor so not sure about the tile choice .

I love Beth H's. design with the decorative tile surround and the new mantle! Would definitely remove the existing hearth and replace with tile to match the surround as Beth H. suggested. Good luck!