I would paint the paneling above the mantle in a color the same color or slightly lighter than your wall color (just go up on the color fan deck selection that has your wall color). The paneling doesn't work with the stone, which is more sophisticated than that country panelling. Since the stone is nice and more messy/expensive to change, and it looks as though it matches the outside fireplace, I would paint that paneling. You can keep the mantle, but see my comments below.

You will need either a mirror (only if there is something lovely that would be reflected in it) or a gorgeous piece of art that is the same width as the below fireplace opening placed over that outlet above the mantle. Hang it about 3" above the mantle, or if it is very tall you can put it down on the mantle.

Also, the windows on each side need window treatments to hide the fact that there is no trim around them. Perhaps drapes that are on both sides plus matchstick blinds to hide the blank wall above the windows. Hang the drapes about 4" from the crown moulding, and hang the matchstick blinds at the same point. It will make it look as though your windows are much taller (but they are just covered by blinds).

Choose the art and the fabric for the drapes in conjunction with the rest of your vision for the room (area rug and upholstered furniture). Pick a fabulous oriental carpet, or a colorful fabric you love, to start the inspiration. Make sure that you include that brown mantle color in the decorating/fabric/rug inspiration. Or paint the mantle too, but I think it is nice to have some contrast there, as long as the brown is repeated elsewhere. You could put two club chairs on either side of the fireplace. That would hide the outlets from view as you came in the room. But the outlets are handy for lamps for those chairs.

Edit to add: this blogger did exactly what I was suggesting with the windows on each side of her fireplace. Like you, she had windows that had a lot of wasted space above them, so she hid it by hanging the drapes high and putting bamboo blinds underneath. You have to scroll down to see her fireplace pictures.

https://theturquoisehome.com/how-to-choose-bamboo-shades/

Wow! Thank you for the very thorough reply. We're about to move in and that's why there's nothing right now. I'm mostly worried about the bottom of the fireplace. Our previous house had a small brick ledge where I placed other decorations. Really just wasn't sure what to put on the floor.

Edit: Thank you so much @lerkat for the link!!!

Yes, I noticed the floor. Usually, there is a hearth slab on the floor in front of a fireplace. It looks as though your fireplace is strictly gas, and so it is not needed. I wouldn't draw attention to it, and concentrate on making the other parts of the room feel great and comfortable.

Once you add your furniture and window treatment, then decide on the floor accessories, if any, given the fireplace’s facade. Benches under windows might be a nice addition instead or add two chairs.