start with walls

I would not paint the brick. I might consider painting the wood but as a last resort. To me it is the curtains that do not fit the room. That print seems too modern.

My first thought was, “wow that is a dark, dreary room”....so, yes! Paint those walls, and the wood too, and then the brick wall at back of room (not the fireplace)...a warm white would be great....right now there’s too much competing for the eye....walls/wood in same color and same for back wall will allow the eye to focus on the floor and whatever furniture you put there.

Assuming you are keeping the floor, yes, paint the walls the lightest color of your brick, maybe even lighter. Paint the lower wood as well so it isn’t so broken up. Leave the brick as is. I would hold off on the curtains until you furnish the rest of the room and then choose an accent color (no pattern) that is also in your rug, pillows etc.

Is the wainscotting wood removable? Thats the first thing I would do, and then patch the holes, sand and prime and paint all the walls, one color. The brick wall by the stairway confuses me. It looks like it doesnt belong and even paint on the brick, wont make it look right. I think the brick on that wall should be removed and the wall sheetrocked and painted like all the other walls. Its a really nice large room. I like the floor. Its all the patterns, that dont go together that keep it from looking pulled together. Once all thats done, give the fireplace a good cleaning and live with it a bit, before you decide to paint it. If you do decide to paint it, use a paint wash, rather than just a solid paint, which to me, makes it look very fake.