I did interior design as a crash course evening class and my advice would be, kids rooms to be as funky as you can go. We did ds2's nursery in 3 paint bands, bottom sandy colour for the sea bed, mid blue wavey lined sea and then paler blue above for the sky. Bought sticker pack from boots (but you can get it loads of places) and made a sea scape.
see this
I almost copied their scene.
I agree that you need to work with what you cannot change or want to change (sofas, flooring, expensive dining furniture, pictures, etc) but I would get a large sheet of A3 white paper and work out an overall colour scheme.
People tend to make each room individual and it doesn't flow or it can even clash! If you have several rooms that lead of the hallway think about how each one will be viewed from the hall.
Look for pattern or shape and try to continue that through. Like if you had those very beautiful leather dining chairs that have a mini scroll at the top then repeat that in wallpaper of a cushion.
Tone on tone works well (think of those dulux colour charts where it starts dark then gets lighter in about 6 shades) or look at a colour wheel and do opposites, or colours next to each other.
Choose paint colour LAST, choose fabric for curtains/bedding/cushions and work around that. There are thousands of paint colours. Put it all on the big piece of A3 paper and see if it all gels.
As you are planning beautiful walnut worktops try to pull that wood throughout, a bowl in the living room or furniture. Pick up the grain pattern and see if any fabrics mimic it.
Good Luck (says Fizzy who has just gutted a house from top to bottom, white bathroom, rest of house in pale coffee colour and associated tones, brown leather sofa -I know so unoriginal now, coffee curtains with chocolate gerberra flower on it, off cream kitchen, bedroom in same coffee colour so that it all flows from downstairs to upstairs)