Credenza underneath it should be 25% wider than the TV.

Coffee table 2/3 the length of the sofa, 1" above or below seat level, no wider than 1/3-1/2 the length between the sofa's arms. I'd say oval with some metal on it.

Remove the desk.

What color/material do you suggest for the credenza?

I would get a painted one in an accent color to add interest to your room. Maybe pick up the blue from the window surrounds. If you know that blue color you might pick up a second hand piece that you can paint (and distress, if you like) to suit your taste. Sideboards and buffets can work too. Just have the TV's width measurement to make sure it is wide enough. When you finish with that, lower your art to be centered 5' above the floor or 5" above furniture.

Although your sofas are a dark brown, here is a design of ours that might interest you. We used a credenza that you might like. Also take a look at the coffee table.

Downtown Townhouse · More Info

Downtown Townhouse · More Info