I would paint the mantel, but not black, since there is already a nearly-black surround that is striking. I would, however, paint the brass black, as I have seen no sign that brass fireplace fittings are coming back (it's lights and bath fixtures where it's been showing up).

As for the TV, is there not plenty of space to put it to one side of the fireplace? Better height for viewing, and lets you showcase some actual art on that focal zone, rather than just setting up two stacked black boxes...

Bigger question: are you doing anything with the acoustic ceiling tile?!?

Drywalling over the ceiling

used the sherwin williams visualizer

Go with the black for sure! What are you going to do about the hearth? You can replace that with a light colored stone - that would look good and give you some contrast. It's a good idea to get rid off the brass/gold ;)