Hard without knowing the style of your apartment. My personal preference is the bottom pic (with flowers). I love the ledge for displaying ornaments and a statement mirror or artwork hung above.

Not for me, I find the concrete floors too harsh, the one good thing about them when they go off trend easy to cover with something else.

The stained glass windows seem to be at odds with the exposed brick, but probably match the original part of the house. If the stained glass windows are giving privacy from an overlooking neighbour I would keep them, and work to make the brickwork more like the original part of the house, so it seems less incongruous. This could be done using a traditional wet plaster or solid plaster technique, which you would need to complete befor your gas insert fireplace is positioned. I would finish it of with a traditional timber fireplace surround and mantle piece, which would be the focal point of a more contemporary room, but link in with the original architecture. Best of luck, Dr Retro of Dr Retro House Calls

It is always a bit difficult when you essentially have three key features (view, fire, TV) that should all have the living area seating orientated towards them. With your current floor plan, I think the logical place for the fire is in the corner to the right of the TV. You may have to ensure that the wall projects far enough that the fire is not in front of the window. This wasn’t the question, but of the two fires that you showed, I preferred the first, more contemporary looking one.