Studio Size 20ft by 10ft Elinchrom 200 or 400?

I am going to turn my lounge into a studio area. it is about 20ft by 10ft. WOuld the Elinchrom 200 be sufficient or do I need the 400 kit. I have a canon 5d and a speedlite 580ex and 580ex11. In all the lighting set ups they mention a light for the background. Does this mean I need to purchase another light?

The D-Lite 2 kit will be enough for a studio of that size. Starting with two lights is all you will need in the beginning (actually, you might want to start off with just one, then introduce the other light for different effects), if you want to add other lights down the track, you can.

As Rudi said, start with 2 lights and get yourself a reflector. You don't always need or want a back light but when you do then you can use 1 light as your main light, a reflector for a fill source and the second light as your back light. You can even add a second reflector to use as a hair light and you can pull off 3 and 4 light shots with only 2 lights.

A pal has the D-Lite 4 kit and it's always under half power. Go for the 2s.

I have the Genesis 200 kit (2 x 200ws monolights) and I find that I'm always at the bottom of the power level. Of course I'm shooting with umbrellas, adn the umbrellas are as close to I can get to my subject without being in the picture. I've never once used them at full power, or had the need to.