Here's how I did the basement, with the red circles denoting where I placed each point. That string continues all the way up the stairs and into the second floor hall.
I generally only add another point when the lights need to turn a corner or when I think it is particularly aesthetically pleasing. I don't think there's a limit on the distance you can put between two points, so for example you could light the entire entrance hallway with just three points placed. The Christmas lights also ignore world geometry (as you can see in my example photo), so if you don't care about aesthetics you don't even have to wind the lights up the stairs like I did, just have them clip straight between floors. If you REALLY want to minimize the number of placed lights, the glow produced bleeds through walls and floors a bit, so if you light up the ground floor well enough, it tends to make the basement and second floor pretty illuminated if a bit dim.
