Mainly furniture. Once it's been sealed with wax or some sort of poly acrylic sealant it can be washed down. It's generally used more for the shabby chic look but you can get a smoother finish by watering it down. The big advantage of using it over other paints is that you don't need to sand or prime, it sticks to pretty much everything including glass, concrete, plastics.

Depends on the overall style that you want to achieve and the scale,style and colours of the rooms leading off the hallway. Remember you will see the other rooms from the hall when the doors are open and vice versa. The creams and biscuits you like will give a classic look and will not jar with the other rooms, if you intend to use bold artwork on the walls then this would then enliven the space. The staircase is fabulous and I agree with the previous comment that a blue would work well with it. Perhaps use a faded ombré look to give more interest a blue low down fading up into white ?

Primed & then an oil based paint

A hammer, chisel and then plaster skim... Seriously - I have yet to speak with a customer who has tried such "refreshes" who has been happy with the result. There is always a first time for everything, though...