Caroline, It appears to me that your image is lighting properly, maybe not as you want it to, but from a engineering point of view it may be fairly accurate. You should read the tutorial on lighting to begin with, and do some experiments with a simple model using from 1 to 4 fixtures just to get the feel for what can be done. Vary the lumen, cone angle, and heights and see what happens. The time spent playing with a simple model, is often much less then a single render of a complicated model. Btw, with as many fixtures as you have, 50,000 lumen is a lot of light. Unless your ceiling is very high, with the number of fixtures you have for a living room setting, I would use between 50 and 500. My guess would be closer to 50 then 500, but you have to experiment.
White is a difficult color for a beginner to master. I also see that you are mixing natural and artificial light together. This can cause problems with shadows. Each light will cast a shadow, so you will get multiple shadows from each chair, etc. Make sure that you do not have any SU default textures, its best to apply a color to every face. Also upgrading to v2 will make life much easier.
What is a "star" fixture and where did you get it?