There are lots of obstacles at the ceiling that have to be addressed. Built ins might not be the best way to proceed.

It would be a lot easier to use these ladder bookcases instead.

You might be able to look at adding some bookshelves to either side of the electric fireplace. It might help it look more like it was built-in. See the below image.

Contemporary Renovation: Family Room · More Info

You could try using the same trim of the fireplace to create a molding accent wall of the same white. Sorry I couldn't match the white and didn't finish all the lines in my render. You could do rectangles instead of diamond shapes and be more like the fp.