It depends on what lights you are fitting, wattage etc. I have put two spots in each of the bedrooms, you could probably get away with one, but don't see why you would, also, unless you move it more central it may not look right - seems a lot more trouble than fitting two.
In the lounge/ kitchen - I would say definately have one in the kitchen, if anything skip one in the louge - but again maybe use single spots in each rather than having to blck them off. Obviously depends on the sort of lights you want!
Ted