Jessica
Just in case, don't buy ebay kits.
Phil is quite right.
For a small studio 200 maybe 300Ws lights are more than powerful enough - What makes the difference is the modifiers you can put on them. Phil has mentioned most of the other important considerations - also important depending on what you are shooting is the flash duration. Some flashes have a burst that is 1/6000th second and allows you to stop action (like dancers in motion). Some cheaper units may have a flash duration around 1/900th and that is not fast enough to stop motion in a fairly fast moving subject.
With low power lights you can also use wider apertures in your images - With 500Ws lights if close up, you may struggle to get below something like f11.
Lots of considerations - 200Ws lights will easily light a white background.
Would be interested to hear what you went with in the end.