Wood. This space needs more medium wood tones to balance out the painted and grey surfaces.

Wood would work, for sure. But now that I see your drawing, plus your red accent pillow, I can’t get the red out of my head. :) So, in other words, I’m probably useless.

You seem to have a mix of styles, which is confusing. Why not pick a style, and invest in a nice piece that will work for you for decades? What pieces do you currently own that you love? Work with that, gradually building your collection over time.

Thinking about this sideboard to soften up the dark brown. would it look weird?

IMO not one more spec of espresso please. It looks cheap and is already a dated finish. Please lower your art work and maybe put the larger one above the new cabinet. I would do maybe white with glass doors and whatever you get needs to have some storage to take care of the kitchen clutter .