rar69-Can you some more photos of your room?

It would be dramatic, but you could get away with it if you hung a big piece of white canvas art on the top- like 36' wide x 48" tall.

and I'd consider a larger carpet 12x9 with similar colors to the art.

I'd like to see a traditional cast iron dog grate in there, or perhaps a small woodburning stove. By adding even more black within the space it will look less blocky.

The artwork or mirror above a fireplace should always be in proportion with the fireplace - nearly as wide as the mantel.

So the brick will be covered up? That makes it harder for me to envisage the end result. Personally I love a bit of exposed brick and it works well with black (I'm looking at my own brick-and-black fireplace!). What colour will you paint the chimneybreast?

A mantelpiece gives you the opportunity to change things around easily when you're ready for an update - add a pair of vases for a traditional look, swap these for a collection of coloured glass bottles for a vintage look, or a pair of silver candlesticks for a formal look.