I like decoenthusiaste's suggestion about priming and getting LED lights, although I like 2700K for my space. Use foam core boards, because one color can negatively effect another. Plus you can move a board around the room. I don't know which color was which so I numbered them I like 3 and 1 the best. I also liked 4, but that might be too dark for your space and the rug doesn't have brown in per se. The mock-up used 3 - pretty perfect.

The best option (the one with the most longevity and flexibility for decorating/changing decor etc...) would be to paint the entire space one neutral color without accent walls. If you must an paint accent wall then please pick the right wall to accent and yes it should go all the way up wherever the wall goes. https://thedecorologist.com/how-to-choose-an-accent-wall/ If you really really still want that wall "accented" (and want the stairway wall a different color than the living room wall) then you could use molding on the wall to create a break point for the color transition.

Here are the colors BM recommends to go with Pine Green: https://www.benjaminmoore.com/en-us/paint-colors/color/2051-20/pine-green In the absence of any context I don't know what else to tell you. How are you using the Pine Green? Are you looking for a complementary white/off white or some other color? What color are the floors and furnishings in this room? Can you post some pictures?

Chair rails belong in a dining room. "Historically, this molding was used as a protective barrier in high traffic areas. Chair rails would protect the walls from any moving furniture to prevent it from hitting against the wall. This is where the molding got its name, since wall damage was typically caused by the back of a chair." If you can pop off the rail do so. As for a color scheme to give you a different look, do grays, purples, dark gold.