I would measure the space from the window, to the first step up and center them to that space. are you planing curtains for the window?

can you stand back and get the whole wall?

You want to treat the wall space that shares the same floor elevation so I would also center your artwork between the window and to the first step.

Could you move the whole sectional to the right or is it centered with the fireplace or something else? It would look better and more balanced if the sofa was in the middle of the blank wall. The end table looks too big and takes up too much space.

The glass top console table is in a bad location. It would work better under the panels or behind the other side of the sofa.

We need to see all of your walls--more pictures please.