We need help choosing a wall paint and floor stain color and any other advice you can give (eg Lighting, rugs).

We are buying a small apartment and want to update it slightly without spending much. We want to get the most bang for our buck.
The walls are beige and the floor is typical NYC parquet. Kitchen cabinets are wood and countertops are some kind of black Galaxy Quartz. We have a white microfiber sofa, and our bedroom furniture is dark wood.
We were thinking about doing espresso stained floors, BM grey owl walls but we don't know how this will work with the kitchen cabinets and built ins. And how will this look with our current furniture? Will a few simple light colored rugs make the space feel bigger?
For our daughters room we were considering a light purple, and a light colored rug to take away from the dark floors.
Lastly- how much should all this cost?
Help please!