Will there be a TV in this room? Have you tried turning the sectional so one side faces long wall. Then you can add a console with TV or art above it and a nice rug to anchor your room.

You'd create the collage where? You'd have to move the tv to do a collage, if you're thinking that it will go in that area.

My favorite way to obtain affordable art is to have a toddler create it. They are great at this. Purchase a huge piece of MDF. You paint it a solid background color. Then you get three sample pots of paint and ask a 4yo to paint a picture of something. You will end up with a great piece of abstract art.

I wouldn’t do shelving at all. IMO they would look random and cheap, like you thought ”oh, this spot seems empty so how about I go buy some shelves and tack them up here.” And then what would you put on the shelves? Little knicky-knackies? The space isn’t even that big - isn’t there a corner right there? Lower the tv and sound bar a bit. They’re floating.