I would not make it look like part of the kitchen. The dark floor is all you need to tie the living area with the kitchen. Too much dark will close the area in, making it feel small. Keep the wall behind the built-ins matching the wall color (or maybe just a shade darker and paint the shelves to match the crown molding.

Yes, build it, and make it white, as your trim is white, so it will work. Just use at least one piece of furniture in the rich brown from the kitchen -- either a table or seating piece.

Oh yes, then come to the next question
I have this old set of red sofa, and my daughter offers to sell me her brown sofa.
What do you think? which should I use for my living room

Kevin, 'white cabinets but do a wood finish for the back of them in the wood color of your floors. ': Do you mean for it to be like the attached photo? with cabinet front paint white? I saw someone had this build in with the entertainment section /or (mantle) in wood color and 2 sides are bookshelves in white, I could not find that picture again.
.

no pic ? Do it all white but just the back wood for interest. Just a thought for a different look.

With r espect to the sofa, you have enough leather I would go for another fabric. Unless you want to use it in another room. They don't go well together.

The sofa question was a either or for the sofas. Not Both.

I think that the arched wall is a focal point of that room and would design the entertainment center with that in mind. How tall will it be? Will you be able to see the arched effect? I would hate for it to be totally lost behind the entertainment center. I would do the center in white but I would have all the shelves/countertops be in a darker stain like mahogany similar to the floor. It is a really pretty combination. I would also include some cabinet doors in this entertainment center to hide the things that you do not want seen all the time. See photo with mahogany countertop for idea.

I wouldn't do a leather sofa from experience and your house is very beautiful by the way.. I would choose blue accents since it would look good with your floors!