Without seeing the whole room, I would select a wall color in the Taupe/Gray/Beige family to compliment the gray of the brick and the beautiful rich red rug.

How about a photo from across the room?

Is this the only window? South facing?

There are many taupes in midtones to sample. Do you have a preferred Brand? Sherwin Williams, Benjamin Moore?

I'd keep the mantel simple. Highlight a couple of your most treasured items.

https://www.wayfair.com/furniture/pdp/latitude-run-35-wide-modern-swivel-upholstered-barrel-chairset-of-2-w119419889.html?piid=1373515827

SW Breakwater is a good place to start. it the value, not necessarily the gray color.

every monitor shows your fireplace in a different tone.

if you can go really dark, Navy is good too, if you want a deep moody room and have natural light beside just that single window.

I personally wouldn't go light unless you love that contrast between the rich red and your british tan.

... I like the BM Squirrel Tail to push the gray more brown. Only you can see what that really looks like.

I am on the fence about painting the brick, but if if will be an improvement I am not opposed. This is the only window in the room and it's west facing.

Painting the brick would be the last thing I would do. Painting walls is relatively inexpensive.

Painting a Brick fireplace is a commitment. It's not ugly, I'd consider changing out the brass surround to a flat black.

I agree with @Lyn Nielson that a matte black insert is more suited to the stone. And I agree that painting the fireplace would not be a good move. In fact it would remove the masculinity of the room. It would be an eww moment. The natural stone likes the leather sofa if you know what I mean. There's nothing wrong with that stone. It's beautiful and masculine without being flashy so your furnishings take first position.
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You asked how to decorate the fireplace. Keep it simple. Below the mantle, if you are going to use the fireplace as I suspect, you might want a fireplace tool kit on one side. It's appropriately vertical for the area below the mantle. How will you light your fires? Long matches in a vase or a lighter on the mantle or hearth or in a nearby drawer? Keep one nearby. Keep it simple and functional. This toolkit is simple.https://www.mantelsdirect.com/products/modern-ember-harriet-5-piece-fireplace-tool-set-in-black

The mantle is high, so you need a single horizontal item above it or on it. Something like grandpa's shotgun, a stuffed fish, a fishing rod, a single branch or piece of driftwood, an evergreen garland in winter, a long musical instrument like a saxophone, didgeridoo, guqin, or zither, a walking stick, single snowshoe, a canoe paddle, a horizontal wood or ceramic tray with the lighter hidden in it. Just think long and narrow and choose something with personal attachment. Pride of place will convey a meaning, so make sure the meaning is relevant to you and hubby. A series of small items isn't a suitable substitute because of the size and natural ruggedness of the stone. Keep it simple and keep the simple dignity of your fireplace.

On the floor to the right, if it seems open, you could have a basket of small logs, or treated pine cones, or a single vertical pillow to sit on the hearth and warm your back. Keep it simple, relevant, and functional.

When the first suggestion you recieved was paint the brick I balked, went back to look at the brick, but still not a fan of that idea. It's a never go back choice. Not one to make your first days in a home. I too would like more views of the room. We are too close to the fireplace to get a good feel for it in the space. Without enough information I think I would look for a black firebox screen to go with the gray brick. As far as decor what do you own you want to display? It looks like you have great wood floors, the curtains appear to be hung to give the room the impression of height--not always a trick that makes sense we need to see the entire window from farther back. I love the vibrant rug and can see black side chairs really helping with a moody look but not sure with your wood color and the sofa.

For the mantel decor agree that it should be simple and things you like - if it were me, I’d prob try to find 3 matte white vases of different heights for a grouping on one side (i love vintage mccoy, west elm has more modern options ) and then do something organic on the other - maybe a shed antler, but it’s personal

i’d be tempted to spray the fireplace cover in matte black for a more rustic look (high heat formula from Rustoleum)

Congratulations on your new home!

Given the height of the mantel, I don’t think any decor will look “great” as it’s too high. Also the sharp corners on the mantel look to be at head height immediately next to the opening into the room.

If/when you have the budget, consider redoing the entire fireplace/surround to a design that will complement your room. In the meantime, spraying the fireplace doors and giving the stone a good cleaning is a simple inexpensive way to improve the look.

Is there any chance that removing just the mantel is an option? Your feeling that the height is wrong is correct. It suits no purpose at that height.

Correcting myself...stain the brick, not paint the brick.

why does everyone want to paint the brick???

@marhop thank you for saying so. Not everyone wants to paint the brick, which...is it really brick? It's stone, right? Why paint stone? Stone is beautiful and natural. I certainly don't want to paint it.

Besides the OP asked for thoughts on decorating it. To me, that is asking about placing items on the hearth or mantle. The mantle is high, creating a horizontal rectangle, so place a single horizontal item on or above the mantle. The high mantle leaves a vertical rectangle below, divided by a firebox, so really two small vertical rectangles. One gets a fireplace tool kit, since hubby put wood in the firebox and it seems there WILL be a fire or two. The other vertical rectangle doesn't even need to be filled. Keep it simple and dignified, respecting the stone.

I wuld remove that mantel and then one nice large piece of art would be nice.

The stone of your fireplace is pretty dark and a bit oppressive (at least in the photo). Might be nice to lighten it up. At the least will suggest a good cleaning. You could also paint or use a German smear technique which is essentially applying mortar in a smeared fashion . The mantle kinda is what it is. Removing it seems rather involved although just from the one photo it is difficult to see exactly how it is connected. There still seems to be space for hanging artwork above the mantle.

The stone seems very dark in the first photo but not bad in the closeup of the rug. I like arcy's idea of using black.

We moved into our home with a dark fake lavastone fireplace and were going to do something with it, but after waiting a year I got used to it and now I like its vintage funkiness.

I would paint the walls and ceiling Alabaster or Swiss Coffee. We did our walls and ceiling in Alabaster and the effect really opens up the room. Flat finish.

With the 3 pictures you posted it's difficult to show the room with the exact position of things but this gives the idea for my suggestions for decor. I'd install a wood mantel over the existing stone one.

I was wondering as well if the mantel could be moved. If not, I'm not sure you have room for art work that wouldn't look squished. Perhaps a faux hanging plant on one side in a light colored vase would help fill the overly large blank space between the firebox and mantel.

Then you could add other decor in varying heights to help detract from the strong horizontal line of the mantel. Add organic shapes to soften the lines.

Here's a wavy candle holder.

Or something like these.

Vintage McCoy vases are sold on Ebay and Etsy - they are really nice. There are also more modern matte white/of white vases that are really inexpensive on Amazon.

Don't remove your mantle without first checking with the fire department and your insurance agent. They have a purpose that has nothing to do with decor.

@kl23-most fire codes are 12" for a mantel above a wood or gas fireplace. This is just poor placement on the part of the person who designed the fireplace. This mantel looks as though it could come down at least 4" if not more.

I love eclectic! Your fireplace is very nice. I would not paint it! These would be my choices... install a light wooden mantle slipcover over the existing mantle, add a colorful painting on the mantle similar to a John Nieto print, a chargeable light above the art and change the brass surround to a black one.

@HU-229802020 That's what I suggested above a few days ago but nobody seems to have picked-up on it...

I didn’t see this! ❤️

The mantle is built in between the stone layers so although I would like to move it lower, I feel it would be a huge undertaking.

I like the idea of changing the brass surround to black and also putting a wooden overlay over the stone mantle. I didn't realize a wooden surround was a thing!

I've gotten some inspiration on how to decorate the fireplace too which is incredibly helpful!

I'm leaning toward alabaster/cream for the walls and black chairs.

Thank you so much for the the photos and ideas. The photos were super helpful to bring it all into focus! :)