Did you save any scraps of wood? I have used a lime wax before. It would make it look like your candlesticks. I’m not a pro, so I would consult someone before using it on a built-in. An espresso stain would match other elements and not compete with the fireplace, but might be heavy. I think you have a very nice balance between dark and light now. If you had continued your baseboard beneath it, I would say paint it the trim color. Probably would still be fine. Hopefully someone will give you some advice on other colors. I would definitely try any stain/wax treatments on scrap first so you know what technique will give you the color you want. You might have to use wood conditioner or do a certain number of coats.

The color of your trim and mantelpiece

Paint it the color of the fireplace surround. I would also lower your tv so it sits about 5-6" above the cabinet, and remove the decor on top of the cabinet so that area doesn't fight your pretty fireplace.

​​Do you intend the fireplace area to be the main focal point? What I see is the fireplace, which is nicely decorated with the mirror Etc, and a rectangular space on either side of it similar in height. If it were me I would try to make the rectangular space on the right side less prominent so that it is more in balance with the one on the left. I agree the TV should be lower. I would paint the cabinets on the right the same color as the walls, but in a different sheen, such as satin. I'm not sure about the darker area behind the TV set. On the one hand, it does help the dark TV set blend in better. On the other hand, the color contrast with the wall draws attention away from your main focal point.

It would appear you have two choices.

What is your floor color? I can’t tell in the pictures. Wondering about the possibility of staining your built-in the same as your floor, like they did here. It’s lighter than yours, obviously, just using it to show the matching aspect:

https://oakstonehomesiowa.com/white-birch-project-living-room/

ETA: And I don’t know how it would look with the wallpaper, just throwing the idea out there.

Beverly’s mock-up shows that the white would look good with everything.