No image?

It kinda has a simple mid century modern vibe..I would remove that insert if possible....add mid century modern style furniture in neutral tones. Small accents of saturated bold colors.

Paint the grout to match the bricks. A chalk paint would be easy.

Don't think a mantel would jibe with the mid-century vibe. I think it looks how it should barring the insert.

No mantel and think long and hard before deciding to paint the brick I love that pic with the 3 pendants