I've had a very similar situation. Brand new linear gas fireplace with marble surround. Within the first few hours of use (two 30-45-minute sessions to burn off the oil) it cracked in 2 places (top/mantel and bottom corner). We are planning to add a heat shield, add another layer of non-combustible board (to get 1" of board thickness) & replace the marble with 4 pieces instead of 1 to allow for expansion/contraction. Any other recommendations?

You probably should paint the brick white to match the walls, but remove the current surround entirely and see how it looks. I like the look below, including the hearth. But if it's not for you, paint the brick white to match your walls. Pick a white that harmonizes with your rich wood floors, which won't look as intense once you paint the walls. You may not need to lighten the floor once walls are painted. It's the orange walls throwing off all the colors. Houssan is right about keeping TV where previous owners have it. You could float your sofa (or two armchairs to face the fireplace) with other seating facing the TV. (Layout as below but TV where they have two art works.)

If you wait until everything is installed, it will be a disaster of poor planning. Your mantel height should be the same height as the top of the shelves along side, and the top of the built in to the left. A single continuous same height, same depth line. If shallower shelves are planned for on top of that fine, but the bases should all be integrated seamlessly, like old Craftsmen homes did. Your designer needs to draw these out as scaled section details NOW.

First of all, I think your room is really very lovely! The ceilings are great, the wood floors are gorgeous, and honestly, I like the wood built ins. I may be biased since I like stained wood in general and I think it can bring a lot of warmth to a room. That said, I can also understand why you might not. Just throwing out some ideas, I do agree with @Lyn Nielson that the mirrors on the built ins are not ideal and I think it would be a vast improvement to cover or remove them. One option might be to remove the entire top portion of the built in and keep the low cabinets. Or keep the upper part, but remove or cover the mirrors. You don't even have to put the glass shelves back! You could put equal sized large art in either of them, or maybe a TV on one side (if you need one) and art in the other. Like @Patricia Colwell I'm not a big fan of small family photos or decorative doo-dads on small shelves. I'd rather see fewer larger pieces. If you do opt to undertake the whole effort, you could certainly paint out the built ins. (Makes me a little sad, but this is your home not mine.) You could also remove the stone and redo the mantle and surround to painted wood. I do think your inspiration is lovely. One thing to consider is that your fireplace chimney is substantially narrower in relation to the cabinets than your inspiration. With the size of the insert edge, you may not be able to do the vertical legs (not sure if that's the right word) of the mantle plus the trimwork plus the tile or painted brick. Also, just a reminder that even if your home was built as late as the 1990s, popcorn ceilings can contain asbestos (from previously manufactured materials). So make sure to get it tested before you begin demo! It's not worth lung cancer for you and your family to proceed without testing. I say this as someone who had popcorn containing asbestos in my previous home.