I would say 4 lights minimum.
If your are going to light a bedroom, 1 or 2 lights would suffice.
For living rooms and dinning rooms 4 is the number.
The thing here is not so much about power but to compliment the space with light that separate the different planes and to add the mood.
Try to do it better than the normal real estate shoot so you can out stand from the crowd.
I would recommend the Elinchrome D-Light for economy and light weight.
