I, too, can appreciate shiplap - but it doesn't match the style of your home, especially if you are adding crown molding! Honor the home's style - it's beautiful as is. Paint all the walls one color, white ceilings (or a very light mixture of the wall paint color).

As for diluting color . . . You cannot simply cut the colorants without understanding the base color and what the colorant is. Example. I have a can of paint here that has 4.25 / 32 Y3 Oxide Yellow 5 / 32 S1 Black 12.125 / W1 White 2.5 / 32 R3 Oxide Red in Base 2 If I cut the formula in 1/2 the white also gets cut in half and I will end up with a color that is darker, not lighter than the original formula. The computer systems are literally doing the math, but not all colorants are equal in strength - red it more transparent than most other colors, yellow is weaker than many other colors, so getting the mix right can be difficult. If you really want a lighter color that is between two shades it can be done, but I generally will buy a sample of the lighter shade and the darker shade and find out if they are both mixed with the same base. If they are in the same base you can play with the colors and mix the lighter and darker colors in different ratios until you find the perfect shade. I use syringes to measure the amounts so I am sure that the ratio is measured accurately. Then I do my own math to determine the amount of each colorant used in the samples and provide the paint store with the base color and the formula that has resulted in the color I want. If they are in two different bases you can do the same thing, but you will need to buy the appropriate amount of each paint and mix them together in a 5 gallon pail with an paint mixer drill attachment or ask the paint store to mix using their mixer. The same applies if you are trying to get a color that is just a tinge more green or yellow or blue than another. Tools like easyrgb have made a lot of this unnecessary - I can find a similar color in another brand and have it matched by my BM or SW paint store.

The modern farmhouse trend of white shiplap feature walls sounds like a version of what you are asking for. Not recommending shiplap, as that was done to death, but it would give you a sense of the effect of different texture/same color. I think texture (or wallpaper) would work better than color, because the way you see color varies from wall to wall with the light. So the difference in paint colors would need to be different enough for it to look like more than that normal variation in how the same color looks on different walls of a room. I'm not sure if you can get enough contrast with whites. Maybe if your definition of white includes sufficiently off whites. Something like white grasscloth wallpaper could be a nice accent. Or a paintable textured wallpaper.

I’m thinking three dark walls. This is B.M. Nocturnal Gray, but just a guess to colors in the paper. You do need some blue undertone to work with what I call the “mean” west light. My go to for west light is Patriotic White, so I moved down the strip to find something darker. This color would show great with the white crib, and you could add a white rug on the floor, and a white lamp on the dresser.