Hi Up,
You and I are color sisters. I have the same colored oak floors, love the terra cotta, greens, golds you have in your pinterest page, too.

I don't have much advice but just know that paint on the walls is super easy to change if it turns out you don't like it.

We have a smallish rancher also. I'm using the rust-terra cottas and greens, browns, off-whites in furniture, wall art, etc. Started out painting our walls Comfort Gray thinking I wanted something a little different with this house. CG is a darkish bluish, greenish gray. Didn't much care for the intensity of the color so we repainted using Rice Grain (sherwin williams) which gives us a little color but isn't overwhelming. Rice Grain plays nicely with the floor, furniture and textiles.

Good luck!

I have white trim, but my cabinets and floors have an orange/red stain and I used BM Grant Beige on the walls. I have lots of red and orange in the house and it goes well with the Grant Beige.

I think the terra cotta would be too much, and the gold would not look good with the carpet. The color you are calling dark turquoise looks not at all turquoise to me, it appears to be a pretty muted blue-grey. I thin this color would look great in your room and you could go a shade or 2 lighter if you wanted.

Whatever color you choose I would paint the window area the same color and not an accent color as it is now, which accentuates the fact that it is short and makes it look a bit awkward. I'd also consider putting simpler window treatments and/or putting them on the inner part of the window bump-out, perhaps fill the area with a window seat and put panels on the inside, like this:

Since there is no architectural interest

You have plenty of architectural interest ... it's called clean lines and simple walls. And that lovely niche.

Is the carpet staying? I see you pinned some oak floor :)

Get the furnishings first and pull paint colors from them. I would paint that window bay an deep color taken from the rugs you show, install shutters or pull-up blinds and place benches in it with cushy seats and extra pillows as a banquette.

If you want a cozier banquette, hanging partial curtains in front of the niche would give it a secluded look.

The rest of the walls, a less intense color taken from the rugs or upholstery fabrics. If the niche is deep grey-blue, make the walls a paler version of that.

The colors you selected are very deep, and the only way to make them work is to amp up the lighting in the room. (Would you consider adding pot lights in the ceiling?) Also the room is not very large so the dark colors will make it feel more enclosed. I would suggest that you pick one color like the gold but in a lighter shade. Then save the turquoise and brick colors for your fabrics and accents in the room...maybe a chair, pillows, drapes. You could nestle a couple of small armed chairs in the nook with a round table in between with maybe a full length table skirt.

Further, if you want to add more architectural interest, you can by adding crown molding. Now's a great time to do that before you paint.

I really like your color choices and don't believe that darker colors make rooms look smaller. They can actually recede the walls to make the room more expansive. I would not chop up the space by painting the window area a different color and would do the whole room one color, using the others as accents in art and furnishings. I think Tinan gave you great advice and examples of window treatments to enhance your room.

The Templeton gray or something similar will look beautiful with the oak floors, but I might go with a lighter shade after looking at this room with TG.