This is kinda neat way to hang pictures on that wall.

You don't want to block the vent but you might want to hide it some. The light switches are in a bad spot for hanging a painting, although that would be my preference. I would suggest you paint the vent and switches the wall color. I see a can light, so it doesn't need a lamp, but does need something tall. Since it is near the shelving, how about a desk and chair with the "kneehole" where the vent is and your lamp on the right end of it? That would be useful, a space filler and allow for the lamp, plus access to books or office supplies stored in the bottom of the built-in - a mini home office!

I painted vent and switches so that looks a lot better...im kind of thinking about cubes for seating as they can be moved toward sectional for additonal bodies.

I'd place: 3 round sculptural pieces, nothing else on that wall. Make templates and arrange and re-arrane with masking tape until you find a good placement.