maybe a area rug and curtains with a pattern...pillows on the couch with gray pattern

I would get an area rug to anchor the furniture and pull the chair onto the rug. Or at least bring them a little closer to the sofa. Are you looking for a console for behind the sofa? and a coffee table?

forgot...suggest a metal with glass coffee table

Since you have so much leather, a glass top would be good. I would also get a mirror for above FP or bigger art, the one there is too small.

Glass coffee table would look great. You need end tables. Everyone needs to be able to set a drink down comfortably.

This has end table you can slide out and use for add'l people

I would buy a square coffee table, about double the width of the current one. The current one looks undersized. Also, a paned top or glass top coffee table would be nice. Since all of your furniture is plain, I would replace the drapes with a pretty stripe, paisley or floral print/pattern. It would help "fill" the space as it is quite plain. It needs to be livened up.

rug