Ideally, I prefer a look with a little more contrast, but it’s your call, and it probably depends on the wood species you plan to use. I like the top two images. In the first the floor is stained darker, in the second the wood looks the same. I don’t like the third image because both the xabinets and the floor are yellow. Also, keep in mind that wood changes color with uv exposure, and that cabinets and floors may age differently.

it used to be a shade or two different from the cabinets. But w all the graining whether straight or gnarled/ knots or no .... etc......with products now you can get differentiation even if the tone is about the same as cabinets......Just depends. / bring samples in / its the only way.

There is no rule. Some people want it to blend and other want contrast. It depends on the overall design of the space.

Yes, no, maybe. Context is key.